He said both the attack on the prison camp and a recent graphic video that appeared to show a Russian soldier castrating a Ukrainian prisoner of war were evidence of Russian violations of international law.
“These inhumane, barbaric acts represent severe breaches of the Geneva Conventions and their additional protocol, and amount to war crimes,” he said.
Kaja Kallas, the prime minister of Estonia, said Russia was responsible for the “mass murder” of prisoners at the camp, an act that she said called to mind “the darkest chapters of history.”
“There must be no impunity for war crimes, just like there can be no return to relations with war criminals,” she said in a statement.
Critics of the Russian invasion of Ukraine pointed to a statement issued by the Russian Embassy in Britain on Twitter as evidence of how Moscow views prisoners of war.
“Azov militants deserve execution, but death not by firing squad but by hanging, because they’re not real soldiers. They deserve a humiliating death,” the embassy said in a post on Twitter, linking to a propaganda video shot in Mariupol.