 An Israeli airstrike on a school turned into shelter in southern Gaza has killed at least 25 Palestinians. Heavy bombardment at the north, meantime, has forced the closure of medical facilities in Gaza City, then sent thousands fleeing new in search of refuge there. The latest ground assault in Gaza's largest city. An effort to battle Hamas militants, the Israelis say, are regrouping in areas that the army had previously said had largely been cleared of the militants.