The attack came the day before children attending UNRWA summer camps will attempt to set a world record for the largest number of children flying kites at the site.

Gunness said the record attempt would go ahead despite the attack, and called on local authorities to investigate the vandalism.

We condemn this attack, which is an attack on the children of Gaza as much as on the United Nations, he said.

We call on the authorities in Gaza to investigate and bring those responsible to account. We will repair and rebuild the damaged infrastructure and go ahead with the event as planned today.

Last year, masked gunmen attacked the camp on two occasions, setting fire to tents, chairs, tables, easels and other equipment.

Those attacks were blamed on Muslim extremists who view the camps as a symbol of Western corruption because boys and girls mingle freely.

UNRWA's Summer Games programme caters to around 250,000 children in the Gaza Strip during six weeks of summer holidays.