Ukraine and western countries are condemning Russia after dozens of Ukrainian soldiers were killed in an attack on a facility where they were held as prisoners of war.

Ukrainian President Volodymyr Zelenskyy said on Friday that more than 50 people were killed in the attack on Olenivka prison in the eastern region of Donetsk.

Ukrainian and Russian officials blamed each other for the shelling.

Zelenskyy called the attack "a deliberate Russian war crime." The intelligence agency of Ukraine's defense ministry says many Ukrainian soldiers captured at the Azovstal steel works in the eastern city of Maruipol were in the prison.

It also says that a private Russian military organization, the Wagner Group, is believed to have carried out the strike.

Russia's defense ministry says the Ukrainian military shelled the prison using a High Mobility Artillery Rocket System provided by the United States.

EU foreign policy chief Josep Borrell issued a statement condemning Russia over the attack.

US Secretary of State Antony Blinken assured Ukrainian Foreign Minister Dmytro Kuleba in a phone call that the US is committed to "hold Russia accountable for atrocities."

The International Committee of the Red Cross said in a statement that "All prisoners of war, wherever they are held, are protected under international humanitarian law" and they "should not be attacked."

Families and relatives of Ukrainian POWs demonstrated on Saturday in Kyiv. Some carried signs reading "Russia is a terrorist state."