"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.

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