Ukraine has compared Russia to ISIS after a video appeared to show Russian soldiers beheading a captive Ukrainian soldier with a knife.
The footage shared on social media allegedly showed a man in uniform beheading a man who wears the yellow arm band of Ukrainian forces. It was not clear where the video came from.
Ukraine's foreign ministry called on the International Criminal Court to "immediately investigate yet another atrocity of the Russian military".
“There is something that no one in the world can ignore: how easily these beasts kill," Ukraine’s Volodymyr Zelensky said.
“There will be legal responsibility for everything. The defeat of terror is necessary."
Moscow said the video was “awful" and that its authenticity needs to be checked.
Ukrainian Foreign Minister Dmitro Kuleba said on Twitter: “A horrific video of Russian troops decapitating a Ukrainian prisoner of war is circulating online.
“It’s absurd that Russia, which is worse than ISIS, is presiding over the UNSC," he said, referring to the UN Security Council where Russia took up the rotating presidency this month.
“Russian terrorists must be kicked out of Ukraine and the UN and be held accountable for their crimes.”
Militants from Islamic State in Iraq and Syria were notorious for releasing videos of beheadings of captives when they controlled swathes of those countries from 2014-2017.
Ukraine’s domestic security agency said it had launched an investigation into a suspected war crime over the video.
“Yesterday, a video appeared on the Internet showing how the Russian occupiers are showing their beastly nature - cruelly torturing a Ukrainian prisoner and cutting off his head," the SBU agency said.
Separately US President Joe Biden will discuss the war in Ukraine with Rishi Sunak when the two leaders meet on Wednesday.
“I expect the leaders will also have the opportunity to touch base on the latest developments in Ukraine including our continuing joint efforts to support the people in Ukraine," National Security Council Senior Director for Europe Amanda Sloat told reporters
Mr Biden is taking part in a three-day Irish tour with a speech to mark the 25th anniversary of Northern Ireland’s 1998 peace deal, the Good Friday Agreement.
