A Russian airstrike ripped apart a theatre where hundreds of people have been living in the besieged city of Mariupol, Ukrainian officials said, as Russian President Vladimir Putin called for a “self-purification” to rid his country of anyone who questions his invasion.

The bombardment Wednesday of the theatre, which had become a makeshift shelter as combat tore across the port city over the past three weeks and made thousands homeless, left many people buried in the burning rubble, Ukraine’s foreign ministry said in a statement. There was no immediate word on how many people were killed or injured.

At least as recently as Monday, the pavement in front of and behind the once-elegant theatre was marked with huge white letters spelling out “CHILDREN” in Russian, according to images released by the Maxar space technology company.

“My heart breaks from what Russia is doing to our people,” Ukrainian President Volodymyr Zelensky said Wednesday night, hours after he delivered a speech via video to the U.S. Congress that garnered several ovations.

The Russian defence ministry denied bombing the theatre or anywhere else in Mariupol on Wednesday.