The European Union is "deeply shocked" at the discovery by Ukrainian officials of mass graves in the recaptured city of Izyum, the bloc's foreign policy chief Josep Borrell said Friday.
His statement came after Ukrainian investigators pulled hundreds of hastily buried bodies from a forest outside the city, in the eastern Kharkiv region.
"The European Union is deeply shocked by mass graves discovered by Ukrainian authorities,..." said Borrell. "We condemn these atrocities in the strongest possible terms.
"Russia's war of aggression against Ukraine has been leaving a trail of blood and destruction across Ukraine," he added.
Kyiv officials say they have counted 450 graves at the mass burial site and found 10 alleged "torture centres" after the Kharkiv region was recaptured from Russian invaders.
"Thousands of civilians have been already murdered, many more tortured, harassed, sexually assaulted, kidnapped, or forcibly displaced," said Borrell.
"This inhuman behaviour by the Russian forces, in total disregard of international humanitarian law and the Geneva conventions, must stop immediately.
On Thursday, EU chief Ursula von der Leyen said she wanted Russian President Vladimir Putin to face the International Criminal Court over war crimes in Ukraine.
In his statement Friday, Borrell said: "Russia, its political leadership, and all those involved in the ongoing violations of international law and international humanitarian law in Ukraine will be held accountable."