KYIV (NYTIMES) - The increasing carnage and destruction inflicted by Russian forces in eastern Ukraine - punctuated by the use of thermobaric explosives that set off huge, destructive shock waves - led to fresh accusations on Friday (May 27) that President Vladimir Putin of Russia was waging a genocidal campaign to wipe out a substantial part of the Ukrainian population.

A new report by international legal scholars and human rights experts said mass killings, deliberate attacks on shelters and evacuation routes, and the indiscriminate bombardment of residential areas by Russian forces had established a "genocidal pattern" against Ukrainians, in violation of the United Nations Genocide Convention.

The report, which warned that Ukrainians were at "imminent" risk of genocide, came as Russian forces captured the eastern city of Lyman after intense artillery bombardments - including from one of the most fearsome weapons in Russia's conventional arsenal, a rocket artillery system firing thermobaric explosives. Also known as fuel-air bombs, these explosives unleash blast waves of extreme pressure and heat, raising the likelihood of civilian casualties in the surrounding area.

Russia "already uses the heaviest non-nuclear weapons against" Ukraine, "burning people alive," Mykhailo Podolyak, an adviser to President Volodymyr Zelensky of Ukraine, wrote on Twitter on Friday about the thermobaric weapons system. He shared a drone video of its purported use in Lyman that showed giant fireballs exploding on the ground in quick succession.

Lyman, with a prewar population of about 20,000, is near a strategic highway and was the second midsize Ukrainian city to fall into Russian hands this week as Moscow seeks to consolidate control over much of the Donbas region. If successful, that drive could give Mr Putin substantial leverage in any future peace talks. Russian forces also appeared poised Friday to capture Sievierodonetsk, the easternmost city still under Ukrainian control.

Local officials said that fierce fighting was underway in Sievierodonetsk and that Russian forces had surrounded two-thirds of the city after shelling there Thursday killed four residents and destroyed 11 apartment buildings and a house.

In Dnipro, in east-central Ukraine, the head of the territorial defense forces said at least 10 people had been killed and at least 30 injured Friday morning when a missile launched from Russia's Rostov region hit a Ukrainian National Guard facility.

Mr Zelensky warned that Russian forces were trying to turn cities and towns in the country's east "to ashes", as he renewed accusations that the forced deportation and mass killing of civilians amounted to "an obvious policy of genocide pursued by Russia".

US President Joe Biden, who last month accused Russia of committing "genocide" in Ukraine, echoed that forceful language on Friday, condemning Mr Putin for his "brutal, brutal war in Ukraine".

"Not only is he trying to take out Ukraine; he's literally trying to wipe out the identity of the Ukrainian people, attacking schools, nurseries, hospitals, museums, with no other purpose than to eliminate a culture," he said in a commencement speech at the US Naval Academy.

The new report on possible genocide by Russia in Ukraine, released on Friday by the Washington-based New Lines Institute for Strategy and Policy and the Montreal-based Raoul Wallenberg Center for Human Rights, lent credence to such claims.

It said rhetoric from the highest levels of the Kremlin and Russian state media denying Ukrainian national identity and dehumanising its people amounted to "state-orchestrated" incitement of genocide.

"There is considerable evidence demonstrating that Russian soldiers have internalised state propaganda and either expressed genocidal intent or carried out atrocities in response to it," wrote the authors, who include former war crimes prosecutors, former ambassadors and Canada's former justice minister.

The pattern of atrocities targeting civilians in Ukraine is comparable to the genocidal acts committed by Myanmar's military against the minority Rohingya group, the report said, quoting from the US fact-finding mission there: "The vastness of the state's involvement is inescapable."

The report of possible genocide came after the prosecutor of the International Criminal Court announced this month that his office had deployed a team of 42 investigators, forensic experts and support personnel to Ukraine to advance investigations into potential war crimes.

Whether the Russian military's actions in Ukraine are ultimately judged to be genocidal, any legal finding of culpability is unlikely to affect the outcome of the war.

It was four years before the first conviction for genocide was handed down after the 1994 slaughter of the Tutsi minority in Rwanda. And it was six years before the first genocide conviction in the systematic execution of about 8,000 Muslim men and boys in the Bosnian town of Srebrenica in July 1995.

Genocide convictions are hard to attain because they require an especially high burden of proof. While the evidence may be there - mass graves, razed villages, witness testimony - prosecutors must show that the perpetrators were committing atrocities with the intent to destroy a particular group.

That process typically takes years, although evidence of atrocities in Ukraine is emerging much faster in an era of drone videos, intercepted communications and satellite imagery.

While the report's authors noted that they were using a lower standard of proof than would be required in international courts, they said there were "reasonable grounds to conclude" that Russia is violating the Genocide Convention, which would require nations to take action.