The US and UN condemned an IAF strike that killed 10 people and wounded about 30 others on Sunday in a UN-run school in the southern Gaza Strip.
In the town of Rafah, where the military has been battling militants, a missile from an IAF aircraft struck the entrance to the school, where Palestinians who had fled their homes were sheltering, witnesses and medics said.
The IDF said it targeted three Islamic Jihad terrorists Thursday morning near the UNRWA school, but that it did not initially appear like the school had been hit. The army said it was still investigating the attack.
The United States criticized the "disgraceful shelling" and urged Israel to do more to prevent civilian casualties in its war against Hamas militants.
State Department spokeswoman Jen Psaki also called for an investigation into recent attacks on UN schools.
"The United States is appalled by today's disgraceful shelling outside an UNRWA school in Rafah sheltering some 3,000 displaced persons, in which at least ten more Palestinian civilians were tragically killed," Psaki said in a statement.
UN Secretary General Ban Ki-moon said that the attack constituted, "A moral outrage and a criminal act." He added that those responsible must be held accountable.
Robert Serry, UN Middle East Special Coordinator, said the school had been sheltering 3,000 displaced persons and the strike caused multiple deaths and injuries.
"It is simply intolerable that another school has come under fire while designated to provide shelter for civilians fleeing the hostilities," he said.
The IDF says Palestinian terrorists fire missiles at troops from the vicinity of UNRWA schools, prompting return fire. On Saturday, Palestinian militants fired 11 mortars from the vicinity of an UNRWA school in the Zeitoun district of Gaza City.
Last Wednesday, at least 15 Palestinians who sought refuge in a UN-run school in Jabalya refugee camp were killed during fighting, and the UN said Israeli artillery had apparently hit the building. The Israeli military said gunmen had fired mortar bombs from near the school and it shot back in response.