The UN agency for Palestinian refugees is investigating the discovery of 20 rockets hidden in one of its vacant schools in the Gaza Strip. The UNRWA condemned the incident as a "flagrant violation" of international law, adding that the rockets had been removed and that the relevant parties had been informed.

Israel regularly accuses Hamas and other militant groups in Gaza of using civilian installations to store and rockets, including during the current conflict, which began on 8 July.

Gaza militants have fired hundreds of rockets since Israel began air strikes and naval shelling, during which more than 220 Palestinian have been killed. Of the thousands of people fleeing the Israeli bombardment, about 22,000 have taken refuge in UNRWA schools.

"Yesterday, in the course of the regular inspection of its premises, UNRWA discovered approximately 20 rockets hidden in a vacant school in the Gaza Strip," the agency said. " UNRWA strongly condemns the group or groups responsible for placing the weapons in one of its installations," it continued. This is a flagrant violation of the inviolability of its premises under international law."

It said the incident was the first of its kind, warning that it "endangered civilians including staff and put at risk UNRWA's vital mission".