The World Health Organization said Israel provided no explanation for barring its partner organizations from the Strip, where the health-care system has collapsed.

Palestinian health officials called on Wednesday for a humanitarian corridor to three hospitals in northern Gaza that have come close to collapse as Israeli troops have cut off the area during almost two weeks of heavy fighting against Hamas.

At least 20 people were killed in an Israeli airstrike on a United Nations Relief and Works Agency for Palestine Refugees in the Near East school-turned-shelter in central Gaza, the Hamas-run Health Ministry in Gaza said. The school was being used to shelter displaced people in Nuseirat camp, health authorities said. It was bombed on Sunday.