MARIUPOL, Ukraine (AP) — A tank emblazoned with a giant Z backs up clumsily in the besieged city of Mariupol, crashing into destroyed buses before letting loose a shell. Later, snipers took aim at medical workers, one of whom was struck in the hip. An Associated Press journalist witnessed tanks firing on a 9-story apartment block and was among a group of medical workers who came under sniper fire Friday in the city completely surrounded by Russian soldiers. The video he shot shows shells exploding as they hit the apartment block, already severely damaged, setting balconies on fire.