Former UN Secretary-General Ban Ki-moon on Tuesday visited a city on the outskirts of Kyiv where hundreds of civilians were found dead following the withdrawal of Russian forces earlier this year.

On a visit to the city of Bucha, Ban told the Associated Press that “all the people killed here without any reason should be fully honored and remembered in the history of humankind.”

Calling the massacre that took place there “a crime against humanity,” he said those responsible should be held accountable.

Ban, together with former Colombian President Juan Manuel Santos, was visiting Ukraine as members of The Elders, an organization founded by former South African President Nelson Mandela that brings together prominent public figures to work toward peace and human rights.

Russian forces have been harshly denounced for killing hundreds of civilians of Bucha in the process of trying to invade Kyiv.

Authorities said 458 bodies were found in Bucha after Russian forces withdrew from the city following 33 days of occupation.