Russia-Ukraine war: Key things to know about the conflict

Russian troops have stepped up their bombardment of the besieged port city of Mariupol, with Ukrainian officials saying a strike flattened an art school used as a shelter by hundreds of civilians. Ukrainian President Volodymyr Zelenskyy early Sunday accused Russia of war crimes over its siege, describing the attack on the city of 430,000 as “a terror that will be remembered for centuries to come.” In his nightly address to the nation, Zelenskyy said Ukraine is interested in peace, and that ongoing talks with Russia are “necessary.” Pope Francis decried the “senseless massacre,” but did not name Russia as the culprit.