The Kremlin-backed separatists in eastern Ukraine say that at least 40 Ukrainian prisoners of war captured during the fighting for Mariupol have been killed by Ukrainian shelling.
Russia and Ukraine accused one another on Friday of bombing a prison in separatist-held eastern Ukraine, which killed scores of Ukrainian prisoners of war.
Russia's defence ministry said Ukrainian forces "fired on the prison where members of the Azov battalion are being held, using American projectiles from the HIMARS system."
It reported that at least 40 Ukrainian POWs were killed and 84 others wounded in the strike on Olenivka prison, while pro-Russian separatist authorities in the Donetsk region put the death toll at 53.
The Ukrainian army says it "never conducts" strikes on civilian infrastructure or prisoners of war.
Prisoners of the Azov Regiment defended Mariupol for three months, alongside other Ukrainian units. They held out in the southern city's sprawling steel mill for nearly three months, clinging to its underground maze of tunnels.
They surrendered in May under relentless Russian attacks from the ground, sea and air.
Scores of Ukrainian soldiers were then taken to prisons in Russian-controlled areas such as the Donetsk region, a breakaway area in eastern Ukraine which is run by Russia-backed separatist authorities.
Speaking about the prison bombing, the Russian Defense Ministry said: "This outrageous provocation aims to scare Ukrainian soldiers and dissuade them from surrendering."
Ukraine denied targeting civilian infrastructure or prisoners of war, stressing that its army "fully adheres to the principles and standards of international humanitarian law."
The Ukrainian General Staff accused the Russian army of being behind this "targeted artillery bombardment", in order to claim Ukraine had "committed war crimes and cover up the torture of prisoners and the executions they perpetrated there."
Russian state television broadcast footage of what they claimed were the charred barracks and the tangles of destroyed metal beds. Images of what appear to be human bodies were shown.
Euronews cannot independently verify these statements.
Moscow has seized on Azov Regiment's far-right connections as proof of its claims that Ukraine was ruled by Nazis and needed to be "denazified" -- one of the main pretexts for the 24 February invasion.
Both Russian and DNR authorities said that some 2,000 Ukrainian soldiers captured in Mariupol would have to "face a tribunal," with many fearing that this would serve as an excuse to execute some of them.