Russia said on Friday that Ukrainian soldiers had executed more than 10 Russian prisoners of war, accusing Kyiv of carrying out war crimes and the West of ignoring them.
The Russian defence ministry cited a video circulating on Russian social media which it said showed the execution of Russian prisoners of war. Reuters was unable to immediately verify either the video or the defence ministry's assertions.
"This brutal murder of Russian servicemen is neither the first, nor the only war crime," the ministry said.
"This is common practice in the Armed Forces of Ukraine that is actively supported by the Kyiv regime and blatantly ignored by its Western patrons."
There was no immediate response from Kyiv, which has said previously it would investigate any alleged abuses by its armed forces. Ukraine has repeatedly accused Russia of war crimes, which Moscow has denied.
The video shows what appear to be Russian soldiers lying down on the ground in Makiivka, in the Luhansk region of eastern Ukraine, after surrendering to armed men with yellow bands on their arms.
Then automatic gunfire rings out and the video shows around 12 bodies. It was unclear when the video was filmed or who filmed it.
The Russian defence ministry said the video showed "the deliberate and methodical murder of more than 10 immobilised Russian serviceman by degenerate Ukrainian soldiers".
It added that the video was a sign of the "atrocious nature" of Ukrainian President Volodymyr Zelensky and his "regime" in Kyiv, and said he would "answer before the court of history and the people of Russia and Ukraine".
Russia's Investigative Committee, which investigates serious crimes, said later it had opened a criminal case into the execution of "at least 11 unarmed Russian servicemen." Investigators were working to identify the people who had filmed the video, it said.
Russian Foreign Ministry Spokeswoman Maria Zakharova said the video was "further evidence of the crimes of Ukrainian neo-Nazis and Ukraine's flagrant violation of international humanitarian law, including the Geneva Conventions".
"We demand that international organisations condemn this egregious crime and conduct a thorough investigation into it," she added.
In a statement to Reuters, Marta Hurtado, a spokesperson for the U.N. Human Rights Office said: "We are aware of the videos and we are looking into them. Allegations of summary executions of people hors de combat should be promptly, fully and effectively investigated, and any perpetrators held to account."
Earlier this week, the U.N. said it had spoken to Ukrainian prisoners of war, captured by the Russians, who reported suffering torture and ill-treatment. It said it had also documented cases of ill-treatment of Russian prisoners of war in Ukrainian facilities.
Matilda Bogner, head of the U.N. Human Rights Monitoring Mission in Ukraine, said the mistreatment of Ukrainian prisoners by Russians was "fairly systematic" while it was "not systematic" for Ukraine to mistreat Russian soldiers.
Reuters