Ukrainian authorities said Tuesday they have discovered about 200 bodies beneath the debris of an apartment building in Mariupol, the southern port city that’s been targeted for weeks by Russian forces.

An adviser in the Mariupol mayor’s office said the bodies were found in advanced states of decomposition and it’s believed that they were left there by Russia’s emergency situations ministry.

The bodies were uncovered as crews were dismantling a destroyed apartment building in the city, the adviser said in a Telegram post that includes graphic images.