Ten men attacked and vandalised overnight a United Nations facility being used to stage summer camps for children in the Gaza Strip, a UN spokesman said on Thursday.
Chris Gunness, spokesman for the UN Relief and Works Agency (UNRWA), which supports Palestinian refugees, said the facility in northwest Gaza was attacked around midnight on Wednesday.
"The attackers damaged a large billboard, burnt a UN flag and torched part of the stage. None of the UN security personnel at the venue were harmed," Gunness said.
The attack came a 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."
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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.
Gaza's Hamas rulers had no comment on the attack.
The Palestinian Centre for Human Rights condemned the attack, saying it was a result of the "state of security chaos and misuse of weapons" in Gaza.
A statement by the rights group called on Hamas to "bring (the) perpetrators to justice and publish the results of investigations."
UNRWA's "Summer Games" programme caters to around 250,000 children in the Gaza Strip during six weeks of summer holidays.
Throughout the camp programme, children have been trying to set world records in fields including dribbling footballs and hand painting.
Thursday's record attempt will see some 15,000 children flying kites at a site near the beach in northern Gaza in a bid to break the previous record.
They hope to break the record set in April last year in China by some 10,465 children.