Armed men have raided a privately-run American school in the north of the Gaza Strip, setting fire to buses and stealing computer equipment.
Several rooms at the school were ransacked
It was the second attack on the school, in Beit Lahiya, in the past two days. On Thursday a rocket-propelled grenade was fired at the building.
Hamas, the group that controls the Gaza Strip, has condemned the attack.
Correspondents say it may have been linked to US President George W Bush's visit to the Middle East.
In another incident, in southern Gaza, a Hamas policeman has been found shot dead.
'Swamps of vice'
The school's director said the attack happened during the night, with armed men locking an unarmed caretaker into a room before going on the rampage. No-one was injured.
"This is terrorism against education," he said as he assessed the damage.
In a leaflet left after the attack, the gunmen claimed affiliation to al-Qaeda and vowed to attack similar targets.
"Polytheists and enemies of Islam are pursuing each day their work to destroy our youths, who are falling by the dozens into the swamps of vice and moral decadence," the statement said.
Hamas vowed to bring the perpetrators to justice.
"Regardless of the reasons - whether to protest, or because of the visit of the American president, this is not a way to express oneself. This is a criminal act," said spokesman Ihab Ghussein, quoted by the Associated Press news agency.
The school is run by Palestinians and has no American teachers, but is part of an association of American schools in the Middle East and uses a US-style curriculum.
Two foreign teachers from the school were kidnapped in 2005, prompting international staff to leave.