Hundreds of civilians were sheltering in the drama theater during the March siege of Mariupol, the southern Ukrainian port city that Russian troops destroyed and now occupy.
Ukraine's southern forces have been striking the island in recent days to take out Russian outposts. Russia's defense ministry said its troops left as a "goodwill gesture."
Russia has been escalating bombardments of Ukrainian cities this week — attacks Moscow says are aimed at military installations but often hit civilian targets instead.
Scores of civilians were feared killed or wounded in the city of Kremenchuk. Ukrainian President Volodymyr Zelenskyy said in a Telegram post that the number of victims was "unimaginable."