GAZA CITY (AFP) – Masked gunmen stormed a UN-run Gaza summer camp early on Sunday and set it on fire, threatening “harsh measures” against the Gaza director of UNRWA, the UN agency for Palestinian refugees said.

The Islamist Hamas movement ruling the impoverished coastal territory condemned the attack and vowed to investigate it but also accused the UN Relief and Works Agency (UNRWA) of exaggerating the incident.

UNRWA spokesman Adnan Abu Hasna said dozens of attackers assaulted a guard, tied him up and left a letter with four bullets threatening the agency’s Gaza director John Ging.

Abu Hasna initially said the entire camp had been destroyed, but an AFP photographer said the damage was mostly limited to a large tent and a few plastic swimming pools.

The seaside camp was one of several set up across Gaza to teach swimming, sports and other activities to some 250,000 schoolchildren during summer vacation and was to open in the middle of next month.

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.

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

“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.”

However, the ministry also said UNRWA had “greatly inflated the incident” as well as the number of people involved. “According to the initial investigation, the perpetrators set fire to part of a tent and left immediately,” it said.

Hamas has done little to impose Islamic law in Gaza, but smaller and more radical groups have carried out a string of bombings of beauty parlours, coffee shops, Christian institutions and Internet cafes.

UNRWA provides food aid, education and health services to more than one million registered Palestinian refugees in Gaza — two thirds of the population of the coastal strip.

It has been a key source of humanitarian aid to Gaza since Israel and Egypt tightened border closures in the wake of the Hamas movement’s violent takeover of the territory in June 2007.

The incident was widely condemned by Palestinian human rights groups and different political factions.