‘It destroys bunkers’: Russia systematically uses thermobaric warheads in Ukraine. (Published 2022) (2024)

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Russia Edges Closer to Seizing Key City in Eastern Ukraine

That has allowed the Russian Army to concentrate its forces in a small pocket of eastern Ukraine, where Russian supply lines are less vulnerable; where Russian forces have shored up their control of some newly captured territory; and where Ukrainian officials say their army is now considerably outnumbered and outgunned.

The latest indicator of this dividend came on Saturday, when two senior Ukrainian officials said that Ukrainian and Russian forces were locked in heavy street fighting inside the eastern city of Sievierodonetsk, where Russian soldiers had advanced to within a few blocks of the administrative headquarters. By Saturday morning, the Russians had captured a bus station and a hotel in the city’s northeast and damaged 14 high-rise buildings during at least three rounds of shelling overnight, the head of Luhansk Province’s military administration, Serhiy Haidai, said.

The last remaining Ukrainian-controlled route into the city was still open, across a bridge spanning a river to the city’s west, said Oleh Hryhory, the provincial police chief. But there was heavy shelling around it, making access to the town extremely dangerous, Mr. Hryhory said.

In his nightly address, President Volodymyr Zelensky of Ukraine said late Saturday that his country’s forces were holding off the Russian assaults on Sievierodonetsk, but acknowledged that they faced “indescribably difficult” conditions.

A railway hub with a peacetime population of about 100,000, Sievierodonetsk is the Ukrainian military’s last significant redoubt in Luhansk Province. While the city is not expected to fall imminently, Russian forces have been making slow but steady gains toward what would be a strategically important victory there.

Its capture would open the way for the Russian forces to set their sights westward to Kramatorsk and Sloviansk, the last major Ukrainian-held cities in the Donbas region, which includes Luhansk and its neighbor Donetsk. Taking them would all but fulfill a goal set forth by President Vladimir V. Putin of Russia on the eve of his invasion of Ukraine in February. Russian-backed separatists seized control in 2014 of parts of Luhansk and Donetsk, and Mr. Putin initially justified his invasion as an attempt to preserve the independence of the two breakaway territories.

Russia’s entry into Sievierodonetsk follows the capture, earlier this week, of Lyman, another strategic city in the region.

In other signs of tightening Russian control in eastern Ukraine, Russian forces reopened a harbor at Mariupol, the Black Sea port that was recently captured by Russia after months of devastating airstrikes and artillery fire that destroyed much of the city. A ship left the port carrying thousands of tons of scrap metal seized from the occupied city, according to Ukrainian officials and a Russian state news agency. It was the first confirmed instance of the port’s use since Russia gained full control of Mariupol.

Ukraine’s president, Volodymyr Zelensky, has repeatedly vowed that Ukraine will retake the entirety of Donbas, rebuffing growing international calls for his country to cede some territory to Moscow in eventual peace talks to end the war.

“Donbas will be Ukrainian,” Mr. Zelensky said in a speech overnight on Friday. For months, Mr. Zelensky has called for heavier weapons to relieve pressure in the Donbas region and turn the tide in the war. United States officials said on Friday that the Biden administration had approved sending long-range multiple launch rocket systems to Ukraine, a move that the Russian foreign minister, Sergey V. Lavrov, has said would be “a serious step toward unacceptable escalation.”

But for now, Ukraine is evacuating civilians from near Sievierodonetsk, in a sign that Ukrainian officials expect further Russian advances in the coming days, amid fears that Russia might encircle the main Ukrainian positions in Donbas.

Out on the highways in Donbas on Saturday, flatbed trucks carrying tanks and trucks towing howitzers rumbled east, suggesting that the Ukrainian military was reinforcing. The Ukrainian Army does not disclose its force numbers but has publicized the arrival of Western weaponry, including long-range American M777 artillery pieces.

Still, military analysts, Ukrainian officials and soldiers on the ground say the Ukrainians remain outgunned by Russia’s far larger arsenal of artillery.

In one engagement on Thursday and Friday in a forest north of the town of Sloviansk, a dozen Ukrainian soldiers were hospitalized with shrapnel wounds after a nearby Ukrainian artillery unit was outgunned by a Russian mortar crew.

Two officers injured in the exchange said Western nations needed to hasten the supply of long-range weapons, including rocket artillery, to even the odds in the battle for Donbas.

“We try to push them back but it doesn’t always work,” said Oleksandr Kolesnikov, a company commander interviewed on a gurney in an ambulance outside a military hospital in Kramatorsk. “We don’t have enough people, enough weapons.”

“You ask how the fighting is going,” Mr. Kolesnikov added. “There was a commander of the company. He was killed. There was another commander. He was killed. A third commander was wounded. I am the fourth.”

The Russian advance has been aided by liberal use of one of its most damaging conventional weapons, the thermobaric warhead, according to Ukrainian military commanders, medics and video from the battlefield.

The weapon, a track-mounted rocket artillery system nicknamed Solntsepek, or the Heat Wave, fires warheads that explode with tremendous force, sending potentially lethal shock waves into bunkers or trenches where soldiers would otherwise be safe.

The missiles scatter a flammable mist or powder that is then ignited and burns in the air. The result is a powerful blast followed by a partial vacuum, as oxygen is sucked from the air as the fuel burns.

“You feel the ground shake,” said Col. Yevhen Shamataliuk, commander of Ukraine’s 95th Brigade, whose soldiers came under fire from the weapon in fighting this month near Izium, a town northwest of Sievierodonetsk.

“It’s a hollow booming sound and the ears ring when it explodes, more than from ordinary artillery,” Colonel Shamataliuk said. “It destroys bunkers. They just collapse over those who are inside. It’s very destructive.”

The United States and other militaries also deploy thermobaric warheads in missiles and rocket-propelled grenades, but analysts say the Russian military’s deployment of the weapon in Ukraine has been among the most systematic uses in recent wars.

But while Russia currently seems to hold the advantage, its advances also come with their own disadvantages. By extending their supply lines, Russian forces themselves become more vulnerable to counterattacks and the logistical complications that plagued Russian maneuvers earlier in the war.

Within Russia, there are also increasing misgivings about whether Russia’s military has the force and resources to continue fighting.

Five opposition deputies in the local legislature of Primorsky Province in Russia’s Far East signed an open letter to Mr. Putin demanding that Russia stop fighting and withdraw its forces. Russia would be better served by using the young men fighting in Ukraine to work in Russia, said the statement read out by Leonid Vasyukevich, a deputy from the nominally opposition Communist Party.

Earlier this week, a diplomat at Russia’s mission to the United Nations in Geneva resigned over the war, the most senior official to leave their post out of opposition to the invasion.

And while it supports the war, a grass-roots Russian movement argues that the Kremlin hasn’t done enough to help its soldiers prepare for a major conflict. Led in large part by women, the group is crowdsourcing aid for Russian soldiers, including food and medical supplies.

Within Ukraine, the war has formalized a long-brewing schism within the Orthodox church. Late on Friday, the leaders of the central branch of the Orthodox church in Ukraine made a formal break with the hierarchy in Moscow.

The Council of the Ukrainian Orthodox Church said on Facebook that it was breaking with the Moscow leadership because it disagreed with Patriarch Kirill I, the leader of the Moscow Patriarchate of the Russian Orthodox Church, over his support for the war.

Patriarch Kirill has repeatedly blessed the Russian military forces invading Ukraine. Because he is the church’s spiritual leader in both countries, many of the Ukrainians dying under the onslaught are his followers. He has also avoided condemning attacks on civilians.

The church has been under the wing of the Moscow Patriarchate for centuries, and its departure will markedly decrease the size of the patriarch’s flock because Ukrainians attend church in greater numbers than Russians.

But it is unclear how many of the bishops and parishes in Ukraine will follow the lead of the council, or how many might try to stick with Moscow.

Disputes within the church, which can last for centuries, revolve around complicated questions of doctrine and authority. The church in Ukraine has been wrestling with an internal split since 2014, the year that Russia annexed Crimea and sparked a separatist war in eastern Ukraine.

Reporting was contributed by Carlotta Gall from Bakhmut, Ukraine; Maria Varenikova from Kramatorsk, Ukraine; Anton Troianovski from Istanbul; Erika Solomon from Lviv, Ukraine; and Nadav Gavrielov and Alexandra E. Petri from New York.

Brittney Griner’s supporters are being more vocal in their efforts to free her.

It has been more than three months since Griner was detained, accused of having hashish oil in her luggage at an airport near Moscow. But only in the last few weeks has there been a coordinated public campaign by W.N.B.A. players and by Griner’s wife, family, friends and agent, Lindsay Colas, to push for her release. That’s where the hoodies — worn by many different players — and the initials — displayed on W.N.B.A. courts — come in. The #WeAreBG hashtag seen on warm-up shirts and social media is also part of the campaign.

The delay in starting the campaign was strategic: Griner’s camp was worried that publicity could make the situation worse because of tensions between the Russia and the United States, including the war in Ukraine. But the delay has also been a source of frustration for women’s basketball players known for their social justice advocacy. Their approach has changed since the State Department said on May 3 that it had determined that Griner had been “wrongfully detained.”

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Long-range weapons take on new import in Ukraine.

On Saturday, Ukraine’s defense minister, Oleksiy Reznikov, said that sophisticated Harpoon anti-ship cruise missiles had arrived. He said the Harpoons came courtesy of Denmark and would be used to try to break Russia’s Black Sea blockade and to protect the port city of Odessa.

The U.S.-made Harpoons were pledged after a virtual meeting earlier this month of the Ukraine Defense Contact Group, a group of dozens of countries that was formed to support Ukraine with military aid.

News that they had started to reach Ukrainian forces came as American officials said the Biden administration has approved sending long-range multiple launch rocket systems to Ukraine, a significant transfer that could hugely aid Ukraine’s defense of its territory in the Donbas region. Ukraine had been asking for the systems, with Prime Minister Boris Johnson of Britain agreeing on Friday that they should be supplied.

Mr. Reznikov confirmed delivery of the Harpoons on the same day that Russia’s defense ministry claimed to have successfully test-fired a hypersonic Zircon cruise missile from the Barents Sea at a target more than 620 miles away.

Hypersonics, generally defined as weapons capable of flying at speeds over Mach 5, or five times the speed of sound, are at the center of an arms race among the United States, Russia and China. Russia has frequently claimed successful test-fires of various ostensibly sophisticated new missiles, and has released images purportedly of Zircon cruise missile tests before.

Both Ukraine and Russia have deployed heavy artillery along the eastern front, with American-made howitzers reaching Ukrainian forces this month. The new, longer-ranged Western artillery are the most powerful and destructive of the many types now being provided by NATO countries. They fire three miles farther than the most common artillery system used by the Russian army in the Ukraine war, the Msta-S self-propelled howitzer — and 10 miles farther if shooting a precision, GPS-guided projectile.

According to Ukrainian and British officials, Russia has been using one of its most fearsome conventional weapons, a rocket artillery system nicknamed the Heatwave, in a systematic fashion. The system fires thermobaric warheads that send potentially lethal shock waves into bunkers or trenches. Such explosives, also called fuel-air bombs or vacuum bombs, scatter a flammable mist or powder that is then ignited and burns in the air.

Zelensky calls fight in Sievierodonetsk ‘indescribably difficult,’ but says Ukrainians are holding on.

With its recent advance on Sievierodonetsk, one of the most important cities still held by Ukraine in the area, Russia has edged closer to occupying the entirety of the Luhansk region.

Mr. Zelensky emphasized that the defense of eastern cities depended heavily on “a supply of weapons” — echoing the words of outgunned Ukrainian officials and soldiers on the ground who have struggled to hold back a ponderous, incremental advance by Russian forces backed by long-range artillery.

Russian guns pounded the city of Lyman for weeks before it fell in recent days, and Sievierodonetsk has increasingly been subjected to the same treatment. Better use of artillery and a deliberately slower tempo of operations has helped Russia advance in the region, according to analysts. In Sievierodonetsk, civilians have for weeks been forced to cower underground in basem*nts or bomb shelters without consistent power, gas or water.

Mr. Zelensky also said that Russia targeted the Sumy region, in the northeast of the country, with missile strikes and that one person died and seven others were wounded in the southeastern city of Mykolaiv after it was hit by Russian shelling. He said that the shells landed in a residential area near a kindergarten.

In his remarks on Saturday night, Mr. Zelensky did not address a Kremlin statement that President Vladimir V. Putin of Russia was “open to renewing dialogue with Kyiv.” The statement described a call Mr. Putin had on Saturday with the leaders of France and Germany, and came after an Italian proposal for a cease-fire and amid growing debate among Western leaders about what an end to the war might look like.

Diplomatic talks between Russia and Ukraine stalled this month, with both sides hardening their stance as they sought to make military gains.

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In a standoff with Russia near Izium, Ukrainian fighters live with constant artillery fire.

While Russia makes town-by-town gains further south, the fighting in this part of the country has become something of a standoff. The natural barriers and the constant artillery exchanges have largely brought movement to a halt.

The Ukrainian Army moved into this area after pushing back Russian forces, recapturing 24 towns and villages in the Kharkiv region, and it still aims to retake Izium. “We are fighting now to liberate Izium, getting ready for the counterattack,” said the commander, who asked to be identified by the name he uses as an artillery officer, Horizon, because of fear of reprisals.

For now, Ukrainian forces have dug in, building trenches and bunkers. Some soldiers have been here for long enough that they have made flowerpots out of wooden ammunition boxes and are growing green onions and radishes in their camp away from the front line.

In places, Ukrainian soldiers have built decoy howitzers with logs for barrels in an effort to trick Russian forces into firing on empty fields. But Russian artillery often pounds real Ukrainian positions, and close shelling is routine. Soldiers try to spend as little time as possible outside when near the front line.

“My apologies for the mess— we had no time to clean up,” said one, Captain Roman, who declined to give his last name due to security concerns, in the root cellar of an abandoned house where he has lived for weeks.

Along the walls were jars of pickled vegetables and a few wooden boxes of potatoes, which had already sprouted and were ready for planting.

Out at the position, Horizon was getting ready to respond to the Russian artillery strike with a Soviet-legacy, self-propelled artillery known as the Carnation, which he had camouflaged in a tree line.

First, he checked to see whether his soldiers had received the correct coordinates and prepared the weapon. Once everything was ready, he ordered the artillery barrage. The gun crew then ran to another tree line and listened to the sky, waiting for what might come back.

Life with ‘the basem*nt dwellers’ of northeastern Ukraine: tremors, grief, community and borscht.

As a woman spooned volunteer-delivered borscht, the staple of beetroot soup, into the bowls each residents keeps for themselves, 4-year-old Nazar Ryabuvo zoomed past on a scooter with light-up wheels.

His mother, Nataliya Ryabuvo, sat on a pallet nearby, shaking.

“My son only knows how to count to 10,” she said. “He often runs out of numbers when he is counting the explosions he can hear in a day.”

Seven years before Russia’s full-scale invasion of Ukraine, Ms. Ryabuvo, 40, sustained her first war injury, a contusion. Though she is from Derhachi, she was volunteering on the front in the east, helping the Ukrainian Army defend the country against Moscow-backed separatists. There, during the monthlong battle of Debaltseve in early 2015, she met her husband, Sergey, a Ukrainian soldier who was wounded in a tank explosion. But as a result of injuries sustained from that time, she began to suffer from epilepsy, and she now she trembles much of the day.

Conditions are difficult in the dank basem*nt, where she and her son are breathing in dust and fumes and she lacks regular access to a shower.

She doesn’t complain though.

“I am healing myself,” she said, though she noted with gratitude that volunteers bring medicine, if not enough.

Crouching on the next pallet and speaking in hushed tones was Shura Hondarenko, whose own makeshift bed stood next to the wall and near the entry. Ms. Hondarenko’s husband, Volodya, died in that bed less than three weeks ago. He had hypertension, and the war and the below-freezing conditions in which they were living did not help, she said.

“In March it was so, so cold,” Ms. Hondarenko, 65, said.

She said her home was still standing, but she was afraid to go back, or to spend much time outside.

“One day a woman named Nadya went outside,” Ms. Hondarenko said. “She never came back. She died in a bombing.”

Both women said the community that the basem*nt dwellers have built over the past three months meant “everything” to them.

“What helps is that we are together,” said Ms. Hondarenko. “We are so grateful for one another.”

“We will be here to the end,” Ms. Ryabuvo replied.

A mile and a half up the road, families were sleeping in a basem*nt built as a bomb shelter for a different conflict, reminders of which survived in Soviet-era posters with instructions and cartoons about how to behave in case of an air-raid siren or a nuclear catastrophe. They were put up when the United States was the expected threat and Russia and Ukraine were united under the Soviet Union’s flag. On Saturday, as the thud of incoming artillery shook the building for the countless time since Russia invaded Ukraine, no one consulted the posters.

Thirteen-year-old Alina Trusova had moved to the shelter from nearby Slatyne, within seven miles of Russian troop positions. Her stepmother, Lyubov Rytava, broke into tears as she described how shelling the previous day had killed a neighbor she had been close with — and convinced her it was time to flee the village after three months of holding out.

Alina’s father, Sasha, suffered a contusion after the shelling but had managed to arrive with Ms. Rytava. In the shelter, he showed off photos of Alina earning an orange belt in karate just before the war.

As she contemplated her prewar life, Alina quietly began to cry.

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Diplomats fear Russia may use Syrian aid as a bargaining chip in Ukraine.

The U.N. Security Council, where Russia wields a powerful veto, will vote in July on whether to keep the aid route open. But the corridor already appears caught up in the fallout from the war in Ukraine and the competing interests of Russia and the United States.

“The war in Ukraine is having wide-ranging implications for Syria — and for the whole region and for the world,” Foreign Minister Ayman Safadi of Jordan said in an interview this month in Washington.

Shrapnel in the forests and shells from the sky: ‘I’ve never seen such hell.’

“You ask how the fighting is going,” said Oleksandr Kolesnikov, the commander of a company of soldiers fighting in the forest, interviewed on an ambulance gurney outside a military hospital in Kramatorsk. “There was a commander of the company. He was killed. There was another commander. He was killed. A third commander was wounded. I am the fourth.”

Out on the highways in the Donbas region, trucks towing howitzers and flatbeds carrying tanks rumbled east on Saturday, suggesting the Ukrainian military was reinforcing its front lines. The army does not disclose its force numbers but has publicized the arrival of Western weaponry, including American M777 artillery guns.

“We needed to move a group to the left flank and they immediately started pounding us with mortars,” said Mr. Kolesnikov. “That is how I was wounded.”

He called for artillery fire from the Ukrainian side to hit the Russian mortar crew, but said the Ukrainian battery was only able to shoot a dozen or so shells, which did not halt the Russian mortar attack.

The deputy commander, Anatoly Ignatyenko, was wounded a day earlier in the same spot. The two soldiers, now off the front line, comforted one another in the ambulance, and Mr. Ignatyenko helped his commander drink from a bottle of water.

Both said President Biden and the leaders of other Western nations need to hasten the supply of long-range weapons, such as rocket artillery, to even the odds in the battle for the Donbas.

“Let Biden not be stingy with weapons,” said Mr. Ignatyenko. Russian artillery attacks were relentless, he said: “There is not an hour without a pause.”

Also on Friday, a Ukrainian logistics unit resupplying the soldiers in the forest suffered losses. Soldiers drove an armored personnel carrier to the position to deliver food and ammunition.

When the soldiers inside stepped out, a mortar landed nearby, killing the commander of the carrier and wounding two others.

“I’ve never seen such hell,” said Mykola Pokotila, a soldier wounded by shrapnel in the forest.

Another wounded soldier, Serhiy Osetrov, sat gingerly in the same ambulance, wincing from shrapnel still lodged in his right leg.

The Ukrainian soldiers were deployed to the forest to repel a Russian advance in the area, on the western edge of the larger battle raging in the east. “We try to push them back but it doesn’t always work,” said Mr. Kolesnikov. “We don’t have enough people, enough weapons.”

Nearby, another more heavily wounded man was wheeled out on a stretcher, his head bandaged. Bloodied field stretchers were stacked up in a line against the wall, traces of the daily cost from the front lines of the Donbas.

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Sounds of bombardment drown out the ‘last bell’ for the final day of school in Ukraine.

Near the front lines of the war in the country’s east, a local official lamented that instead of the bell, children were hearing gunfire and explosions.

“The last bell did not ring today in Luhansk region,” Serhiy Hadai, the head of the region’s military administration, wrote on his Facebook page. “Those children who still remain in the area’s bomb shelters listened to the cannonade.”

In Luhansk, which is on the verge of being taken over by Russian troops as the city of Sievierodonetsk makes its last stand, schools have been reduced to “empty brick boxes” with wind whistling through shattered windows and desks scorched down to their metal frames, he wrote.

In three months of war, parents and teachers have been scrambling to provide education for Ukraine’s 5.5 million school-aged children through a patchwork of online and in-person instruction and even makeshift classrooms in subway stations, where civilians have been sheltering from Russian shelling.

Any semblance of continued schooling can be helpful to provide children with some stability and to give them a safe space to process trauma, experts say.

Ukraine’s education ministry said that some students would have their classes continue into June because the war had interrupted their instruction.

“Despite the war, the last bell will ring,” the education minister, Serhiy Shkarlet, told students in a speech on Friday. “But it will not be heard by those children and teachers who were killed by the Russian occupiers. We will always remember you.”

The United Nations has confirmed the deaths of 261 children in Ukraine since Russia’s invasion but warned that the true toll is likely far higher.

One school in a small town in western Ukraine wrote on its Facebook page that students had tuned into a tearful online ceremony on Friday from Bulgaria, the Czech Republic, Estonia, Finland, Germany, Ireland, Italy, Poland, Portugal and Spain.

The United Nation’s Children’s Fund also livestreamed a last-bell ceremony for the country’s children, featuring a pop-star-turned-soldier, a professor who has continued teaching from the battlefield and the frontman of the band Kalush Orchestra, the winner of this year’s Eurovision Song Contest.

The agency has previously said that two-thirds of Ukraine’s children have been displaced from their homes by the war.

“The war has changed the daily lives of our children,” Antonina Ulyakhin, a regional politician in Dnipropetrovsk, wrote in a post marking the final day of school. “Many children were forced into adulthood early.”

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Russia plays to its strengths in the fight for Donbas.

Those recent gains are evidence of weakness as much as strength, in that they suggest an army reliant on artillery in order to conserve its forces. But they also underscore how Russia has more of an advantage in Donbas than elsewhere in Ukraine, with concentrated firepower and shortened supply lines helping its forces make progress toward a handful of key cities after a series of costly setbacks in the early weeks of their invasion.

The capture of Lyman also gives Russia access to a major railway junction, as well as to bridges over the Siversky Donets River. That could give Russia an advantage as it seeks to advance on Ukrainian-held cities like Sloviansk and Kramatorsk, a British intelligence report said on Saturday.

In recent weeks, Russia’s military leaders have also “focused on tactics that are better suited to their level of training,” said Jack Watling, a senior research fellow at the Royal United Services Institute, a London think tank. He pointed to better use of artillery and a deliberately slower tempo of operations as improvements.

“The dynamic is that the Russians can advance so long as they can prepare the ground with artillery and essentially drive the Ukrainians off the position,” Mr. Watling said. “But it means that they lay waste to the ground, so they can’t use buildings or towns that they capture.”

Mr. Watling estimated that Russian forces could now be advancing at a rate of just over a mile per day. That pace — along with the gradual influx of heavier weapons to the Ukrainian side, which raises the possibility of a counteroffensive in late summer — means that Russia’s advance is partly a race against time, he said.

There are also challenges for military leaders in Kyiv.

Sievierodonetsk is difficult to resupply by air or road, so they must decide how much to commit in terms of personnel and resources to defend the city and slow Russia’s advance. Although Ukraine paid a high price for its dogged defense of the port city of Mariupol, which fell to Russia this month, for weeks its resistance there effectively engaged Russian forces who could otherwise have been deployed elsewhere.

The withering assault on Mariupol, a city whose gradual destruction at the hands of Russian artillery became a symbol for Ukraine’s suffering, could be repeated in Sievierodonetsk.

“Russian forces have performed poorly in operations in built-up urban terrain throughout the war to date and are unlikely to be able to advance rapidly in Sievierodonetsk,” said a report by the Institute for the Study of War, a Washington think tank.

‘It destroys bunkers’: Russia systematically uses thermobaric warheads in Ukraine.

“You feel the ground shake,” said Col. Yevhen Shamataliuk, the commander of Ukraine’s 95th Brigade, whose soldiers came under fire from Russia’s Heatwave weapon in fighting this month near the town of Izium.

“It’s very destructive,” Colonel Shamataliuk said. “It destroys bunkers. They just collapse over those who are inside.”

The United States and other militaries also deploy thermobaric warheads in missiles and rocket-propelled grenades. And Ukraine’s Army said on April 5 that it had fired Heatwave thermobaric rockets from a captured system back at Russian troops, intending to burn them with their own weapon, in fighting near Izium.

Thermobaric weapons are not banned, and they are not addressed in the Geneva Conventions, a series of international agreements that govern warfare. Russia’s military has deployed the Heatwave weapon in the war in Syria, but its use in Ukraine has become systematic, according to the Ukrainian military and video footage of strikes on towns in eastern Ukraine.

Such explosives, also called fuel-air bombs or vacuum bombs, scatter a flammable mist or powder that is then ignited and burns in the air. The result is a powerful blast followed by a partial vacuum as oxygen is sucked from the air as the fuel burns.

Ukrainian soldiers who have been caught in the explosions and survived suffered a mix of burns and concussions, said Sgt. Anna Federchuk, an ambulance medic based in Kramatorsk, in eastern Ukraine, who has treated casualties from Heatwave strikes.

“It’s a mixed diagnosis,” she said of the typical casualty from a Heatwave explosion. “The burns are deep and severe.”

The Russian weapon carries a box of rockets atop a tanklike tracked vehicle. It can fire single rockets or a terrifying volley. Still, like many Russian weapons deployed in the Ukraine war, the Heatwave system may not be as effective or decisive in combat as Russian military propaganda suggested it would be.

Developed in the 1980s and once viewed as an awesome and feared invention of late-Soviet military prowess, the Heatwave, formally known as a Tos-1 heavy flamethrower, has drawbacks.

With a range of only six miles, it must be driven close to the front to fire. There, it has been vulnerable to Ukrainian ambushes. In March, a drone video showed Ukrainian soldiers blowing up a Heatwave weapon during an ambush outside the Kyiv suburb of Brovary.

The strike on the vehicle sent its rockets sailing out into the Russians’ own column of armored vehicles, though it was unclear whether any were destroyed.

Their use near the front has also allowed Ukraine to capture some of the weapons. Videos have appeared online purporting to show Ukrainian tractor drivers towing captured Heatwave weapons away from the front. Ukrainian soldiers have claimed on social media to have seized five of the weapons systems as trophies.

Ukraine’s military has also said that the Russians have suffered friendly fire incidents with the Heatwave as it sprayed out highly destructive but unguided rockets.

“The leadership of the 97th Infantry Battalion expresses its satisfaction with the actions of the Russian occupiers,” the Ukrainian military said in a sarcastic statement on May 8 after what it said was a friendly fire strike in the Zaporizhzhia region that killed Russian soldiers. “Such actions are positively perceived and supported in every way by the Ukrainian military. We understand there is a tradition of cooking shish kebabs in May.”

Maria Varenikova contributed reporting.