More than 60 people were feared dead Sunday after a Russian bomb flattened a school being used as a shelter, Ukrainian officials said, while Moscow’s forces pressed their attack on defenders inside Mariupol’s steel plant in an apparent race to capture the city ahead of Russia’s Victory Day holiday.

Russian troops launched a wide-ranging attack on Ukraine on Thursday, as President Vladimir Putin cast aside international condemnation and sanctions and warned other countries that any attempt to interfere would lead to “consequences you have never seen.”