A protest was held in downtown Zagreb on Sunday over the massacre of Ukrainian prisoners of war, killed in an attack on a prison run by pro-Russian separatists in Olenivka, in Russian-controlled Donetsk, with protesters demanding condemnation of Russia's actions.

Fifty-three Ukrainian prisoners of war, defenders of Mariupol, were killed in the attack, including members of the Azov Regiment.

Ukraine and Russia blame each other for the attack.

Speaking at the protest, organised by the Ukrainian Embassy, Ambassador Vasily Kyrylych called Russia a hotbed of terrorism.

Russians support a brutal policy of destruction of everything, including schools and kindergartens, he said.

Identifying Russia as a terrorist state is not only a symbolic gesture, it is a strong message of support to Ukraine, the ambassador told reporters, thanking Croatia for supporting Ukraine and taking in more than 20,000 Ukrainian refugees.

An MP of the DP party and war veteran from the eastern Croatian town of Vukovar, Stipo Mlinaric, was among the protesters.

Russia has done to Mariupol what the Yugoslav National Army (JNA) did to Vukovar. Russians shelled the prison to cover up the crime, Mlinaric said.