A UN probe into the Israeli offensive against Gaza finds Israel guilty of intentionally shelling a UN-run school and killing three people seeking shelter there.

The raid was one of eight occasions where the Israeli army targeted UN personnel or facilities, prompting the international body to launch an inquiry into the war crimes committed during the weeks-long onslaught in which more than 1,350 Palestinians were killed.

The three-member UN board of inquiry declared Israel had repeatedly breached the inviolability of UN premises and exhibited "reckless disregard for the lives and safety" of civilians in a separate strike on an elementary school, which took the lives of two children and injured 13 others.

The inquiry board dismissed Israel's defense with its confirmation that there was no evidence that Palestinian fighters had used UN facilities to launch military attacks against Israeli troops.

United Nations Secretary General Ban Ki-moon said he would pressure Israel to pay compensation in excess of the $11 million in damages caused to UN property.

The UN chief, however, rejected the board's recommendation to expand the investigation into other examples of war crimes during the conflict and to hold perpetrators accountable.

"I would emphasize that a board of inquiry is not a judicial body or court of law," said Ban in a 27-page summary he released of the 184-page report. "It does not make legal findings and does not consider questions of legal liability."

Instead, Ban said the UN and Israel would begin negotiations to determine how they can improve their lines of communication to avoid such incidents.

Israeli spokeswoman Mirit Cohen welcomed Ban's assurances but labeled the UN board's report as "tendentious" and "patently biased".

In its report, the board rejected allegations that the three young men killed by an Israeli airstrike against Gaza's Asma elementary school were engaged in military activities, concluding that "it is more probable that they were going out to use the toilets" when they were killed.

They also demanded Israel to publicly withdraw assertions that Palestinians had fired from within the premises of a UN-run school and a UN relief office.