Ukrainian authorities have found a mass grave with more than 440 bodies in the eastern city of Izium, which was recovered from Russian forces, a regional police official said on Thursday, adding that some of the people had been killed by bombing and air strikes.

Serhiy Bolvinov, the chief investigator of the Kharkov region police, told Sky News that forensic investigations would be carried out on all the bodies.

“I can say that it is one of the largest burial sites in a big city in the liberated (areas)… 440 bodies were buried in one place,” Bolvinov said.

“Some died from artillery fire… others died from air strikes,” he said. Thousands of Russian troops fled Izium last weekend.

President Volodymyr Zelensky blamed Russia and compared the discovery to what happened in Bucha, outside the capital kyiv, in the early stages of the invasion by Russian forces in late February.

Ukraine and its Western allies have accused Russian forces of committing war crimes in Bucha.

“Russia is leaving death behind everywhere and must be held responsible,” Zelensky said in a video address.

Russia has repeatedly denied targeting civilians or committing war crimes.