The IDF said it completed an investigation into the shelling on Thursday of an UNRWA school in Beit Hanoun, northern Gaza, and found that Hamas terrorists fired at the army from within the school complex. The terrorists fired anti-tank missiles at soldiers, the army added.The IDF fired several mortar rounds in response. One IDF mortar fell in a yard near the school, which was empty, according to the military."In light of the results of the investigation, claims that people were harmed inside school grounds, as presented after the incident by some, have been ruled out. The IDF regrets every harm to civilians in combat, but stresses again that this is the sad result of Hamas's decision to use the civilian sphere as a human shield," the army said.On July 24, a projectile struck a complex containing a UN school in Beit Hanun in northern Gaza on Thursday, killing at least 15 people and wounding dozens more, according to Palestinian medical sources.The school had served as a shelter for internally displaced Gazans.Related: Terrorists fire anti-tank missile from Al-Wafa hospital in Gaza The IDF launched an investigation, and army sources said it was unclear whether the area was hit by an Israeli or Palestinian range projectile.Later Thursday night, the IDF said an initial investigation found that terrorists had opened fire from the vicinity of the school, and that the army returned fire. At the same time, Hamas fired in the general direction of the school, the army said. Civilians in the school were asked to vacate the area, but refused, the army added.