The IDF denied a report on Sunday that an errant Israeli mortar shell was behind a deadly strike that killed 39 people at a school in Jabalya run by the United Nations Relief and Works Agency last week. According to The Associated Press report, Israeli defense officials have said in private that at the time of the attack, the IDF was returning fire at Hamas men who had just fired a rocket at Israel. The army fired three mortar shells, two of which hit the target and one missed by about 30 meters, causing the casualties at the school, whose number the IDF believes was inflated by Hamas. "We are still sticking by our official position that according to our initial inquiry, the whole thing started when terrorists fired mortar shells from the school compound [at soldiers]," Capt. Ishai David told The Jerusalem Post. "The IDF returned fire to the source, and the unfortunate result was the death of innocent civilians," David said. He added that two terrorists, who were part of a Kassam squad, were also killed in the incident. UNRWA has insisted that there were no terrorists in the school compound. Already last week the aid organization told the Post, "The Israeli army in private briefings with diplomats have admitted that the militant fire from Jabalya yesterday came from outside the UNRWA school compound, and not from inside the UNRWA school compound," spokesman Christopher Gunness said. "This allegation against UNRWA is completely baseless," he said. Also on Sunday, at a press conference in Jerusalem, UNRWA claimed it was IDF gun fire that killed a Palestinian truck driver working for the aid group near the Erez crossing on Thursday. "Given the location where the incident took place, the shots could only have come from the IDF," said Aidan O'Leary, UNWRA's deputy director in Gaza. O'Leary added that a meeting with the IDF on Sunday, the officers "shared with us a deep apology for the loss of life." But Capt. David told the Post on Sunday that "the initial inquiry indicates that it was not IDF fire that killed him." Last week a MDA medic at the scene told the Post that soldiers in the field said Hamas snipers targeted the aid workers. Two Palestinians wounded in the same incident were treated at Barzilai Medical Center in Ashkelon. AP contributed to this report.