Ukraine has launched an investigation after a video emerged purportedly showing Russian troops killing two Ukrainian soldiers who had surrendered.
Ukrainian prosecutors say the footage shows "a group of people in Russian uniforms" shooting the unarmed Ukrainians at close range.
The prosecutors say the killing of prisoners of war is a "gross violation" of the laws and customs of conflict.
The video has not been independently verified. Russia has not commented.
Since Russia launched its full-scale invasion in February 2022, both Kyiv and Moscow have accused each other of violating the Geneva conventions - a set of international humanitarian laws regulating the conduct of armed conflict, and specifically the treatment of POWs.
In a statement on Sunday, Ukraine's prosecutor general's office said a pre-trial investigation was launched "for violation of the laws and customs of war, combined with intentional murder".
It said the killing of POWs qualified as "a grave international crime".
Preliminary data suggested that the shooting happened near the village of Stepove in Ukraine's eastern Donetsk region, the office added. It gave no details about who shot the video and when.
The area has seen fierce fighting in recent weeks, as Russian troops have been attempting to seize the nearby town of Avdiivka - a Ukrainian stronghold just outside the Russian-held regional capital of Donetsk.
In a separate statement on Sunday, Ukraine's military urged the world community to "condemn Russia's actions and bring to justice the military leadership of the aggressor country".
Russia's military is yet to publicly comment on the allegations.
What is known about the video
The grainy footage was published by Ukraine's DeepStateUA Telegram channel on 2 December.
It said the two Ukrainian soldiers were shot dead near Stepove, after Russian troops had seized the positions of Ukraine's 45th Rifle Battalion.
DeepStateUA said the Ukrainian soldiers had been forced to surrender after running out of ammunition.
The video itself purportedly shows a Ukrainian soldier coming out of a dugout to surrender. He is holding his hands on his head as what Ukraine says were Russian soldiers point their weapons at him.
The Ukrainian soldier is then seen lying down on the ground face down, and a second Ukrainian soldier emerges from the dugout. None of them appear in the video to be armed.
Just seconds later, the soldiers are seen opening fire on the Ukrainians, killing them both.
The authenticity of the footage has not been verified by the OceanNewsUK.
Later that day, Ukrainian serviceman Oleksandr Kolym said the shot Ukrainians had been from his unit.
And on Sunday, the head of Avdiivka's military administration, Vitaliy Barabash, told Ukraine's Freedom TV channel that those who had carried out the shooting were later "liquidated" in a Ukrainian attack.
Mr Kolym and Mr Barabash provided no evidence to back their claims.
In April, Ukrainian President Volodymyr Zelensky called on world leaders to respond after a video emerged apparently showing a Ukrainian soldier being beheaded by a Russian serviceman.
Russia said at the time that the footage was "awful" but its authenticity had to be checked as well as who was behind it.
In March, Ukraine accused Russian soldiers of killing an unarmed Ukrainian soldier, who was videoed smoking a cigarette and shouting "Glory to Ukraine" before being gunned down.
Late last year, Moscow accused Ukrainian forces of executing a group of Russian prisoners.
It followed the emergence of a video from the front line in eastern Ukraine showing the apparent surrender of a number of soldiers in an incident that ends in their deaths.
A Ukrainian official claimed the surrender had been "staged" by Russian troops in an attempt to attack their captors.
