An estimated 300 people were killed in an attack on Mariupol’s Drama Theater, which hundreds of people had been using as a bomb shelter, local officials said on Friday.

It was unclear how officials had arrived at that estimate. Russian advances in the southern port city have hindered efforts to find survivors in the rubble since the building was largely destroyed in the attack, which occurred on March 16.

The city, one of Ukraine’s largest, has also been cut off from water, electricity and communications during the fighting, although Ukrainian officials have said that about 130 people were rescued from the theater. Ukrainian officials have attributed the damage to a Russian strike.

“Until the last moment, we want to believe that everyone managed to escape,” the City Council wrote on its Telegram channel about the building.

The theater was struck even though the word “children” was written in large white letters on the ground at either end of the building.

“There cannot and never will be an explanation for this inhuman cruelty,” the Council wrote. “As there never will be forgiveness for those who brought devastation, pain and suffering to our home.”