Kyiv opened a war crimes investigation Sunday after two separate reports of Russian troops shooting captured Ukrainian soldiers emerged.
Ukraine's army on Sunday posted a grainy video shot from the air of what it said was a Russian soldier shooting two Ukrainian soldiers at point-blank range.
In the video, two soldiers labelled as Ukrainian advance towards another labelled as Russian in a trench.
They then appear to stop before the Russian soldier grabs and shoots them repeatedly, including while they were lying on the floor, not appearing to resist.
AFP could not verify the authenticity of the video, its location or when it was shot.
"This morning... the Russians once again showed their attitude to international humanitarian law by shooting two Ukrainian prisoners of war," Ukraine's ground forces wrote on Telegram in a post accompanying the video.
Ukraine's Prosecutor General said later on Sunday it had opened an investigation into possible war crimes based on the footage.
It said the incident happened near the village of Vesele in Ukraine's Donetsk region.
The prosecutor also said it was investigating reports of the alleged execution of six wounded Ukrainian soldiers left behind during Kyiv's withdrawal from Avdiivka.
The DeepState Telegram channel, seen as close to the Ukrainian army, reported that Russian forces had shot six injured Ukrainian soldiers, most likely on Thursday, who were too badly wounded to leave their positions during the hasty exit from the town.
It said their fellow soldiers had subsequently recognised their bodies on a video posted on Russian social media.
"The killing of prisoners of war is a gross violation of the Geneva Convention relative to the treatment of prisoners of war and a grave international crime," Ukraine's prosecutor said in a statement Sunday.
There was no response from Russia to the allegations.
Moscow and Kyiv have several times accused each other of violating international humanitarian law by killing prisoners of war since Russia invaded.
The United Nations has documented cases of summary executions of captured Ukrainian soldiers as well as torture during the two-year war.