The fate of hundreds of Ukrainian civilians in Mariupol was unclear early Thursday after Russian forces bombed a theater where they had been sheltering from fighting over the southern port city.

Mariupol has been the target of relentless shelling by Russian forces seeking to advance along Ukraine’s southern coast.

Satellite images from before the bombing showed the word “children” written twice, in Russian, on either side of the building in the city. The entrance to a bomb shelter under the theater was blocked by rubble when the building partially collapsed, said Pavlo Kyrylenko, head of the regional military administration in the eastern region of Donetsk. Former governor Sergiy Taruta said on Thursday the bomb shelter had remained intact, and there were survivors.

Ukrainian officials said a Russian bomb destroyed a theater in Mariupol where hundreds of residents took refuge; President Biden said he thinks Vladimir Putin is a war criminal; Ukraine forces continued their counteroffensive in key cities as the war entered its fourth week. Photo: Donetsk Regional Administration/Reuters

A resident of Mariupol who escaped the city told a Ukrainian TV channel there had been more than 1,000 people in the theater before it was bombed, sheltering in an underground bunker, in the main auditorium and on stage.