The Ukrainian army said Saturday it was checking the authenticity of footage that Moscow says proves Kyiv executed several surrendering Russian soldiers.
Videos circulated on Russian social media this week that purport to show the bodies of Russian servicemen killed after surrendering to Ukrainian troops.
The Russian defence ministry said Friday the videos showed the "deliberate and methodical murder of more than 10 restrained Russian soldiers".
"Before launching an investigation, there must be grounds for it. We are currently establishing whether these videos are fake," Ukraine's spokesman for the general staff Bogdan Senyk told AFP.
Senyk said the videos were "given to specialists", noting the publication of fake videos has "intensified recently".
Russia said Friday the videos represented a "war crime", the latest allegation of abuse after months of fighting in Ukraine.
One video shows soldiers apparently surrendering to several military personnel in camouflage and wearing yellow armbands.
The soldiers who are giving themselves up lie down on the ground in the debris-filled backyard of a house.
The video abruptly cuts off as shots are heard.
Another video filmed from above shows the bodies of around a dozen people surrounded by apparent blood stains.
AFP has not independently confirmed the videos and the Russian defence ministry did not say when the footage was captured.
"We are aware of the videos and we are looking into them," a UN spokesperson told AFP, calling for the perpetrators to be held to account.
The Russian Investigative Committee, which probes major crimes, said it opened a criminal case into the "execution of captured Russian servicemen".
Moscow's claims come after the UN this week published a report saying prisoners of war on both sides had been subjected to torture and ill-treatment.