Rescue workers are searching for survivors in the rubble of a theatre in the besieged city of Mariupol, after Ukraine said a powerful Russian air strike had hit the building where hundreds of people had been sheltering from the war. The port city is encircled by Russian forces and has seen some of the fiercest bombardment of the conflict.“The heart is breaking from what Russia does to our people, our Mariupol, and our Donetsk region,” Ukrainian President Volodymyr Zelenskiy said in a late night address on Wednesday, after referring to the theatre attack. Petro Andrushchenko, an adviser to the …