Dozens of masked gunmen stormed a UN-run Gaza summer camp today and burnt it to the ground, threatening “harsh measures” against the Gaza director of the UN refugee agency.

The attackers assaulted a guard, tied him up and left a letter with four bullets threatening UN Relief and Works Agency (UNRWA) Gaza director John Ging, according to agency spokesman Adnan Abu Hasna.

“The armed men torched the camp, which contained recreational equipment and (plastic) swimming pools, and completely destroyed it,” Abu Hasna said, adding that UNRWA had planned to open the camp in the middle of next month.

Abu Hasna said the gunmen blocked Gaza’s main coastal highway before destroying the facility, one of the largest of several summer camps across the territory catering to some 250,000 Palestinian refugee children.

No one claimed the attack but it appeared to have been carried out by Islamic extremists who have attacked Western symbols in Gaza in the past and are opposed to the camps because they allow boys and girls to mingle.

Mr Ging later told reporters that the attack was carried out by people with an “extremist mentality” and vowed to continue his agency’s work in Gaza.

“UNRWA will not be intimidated by these attacks. UNRWA will repair this location,” he said.

Gaza’s Hamas-run police force was investigating the incident, and interior ministry spokesman Ihab al-Ghussein said “the action is strongly condemned and those behind it will be held accountable.”