Gunmen from a religious extremist group opened fire and threw grenades at the entrance to the school in the southern town of Rafah as students, parents and teachers were leaving after a party, they said.
The dead man was identified as Majid Abu Shamallah, a bodyguard with an official from president Mahmoud Abbas' Fatah party who was at the event.
John Ging, Gaza director of the U.N. Relief and Works Agency (UNRWA), was at the school when the attack was carried out but "he is all right," an official with the agency told AFP.
Three of the alleged gunmen have been detained by Palestinian security forces, a security source said.
"As the party was ending and people, parents and children were leaving the school, the Salafist group threw two grenades and opened fire," a security source said.
A group that described itself as Salafist, a strand of puritanical Islam, on Saturday "sent a statement threatening to sabotage the celebration organized by UNRWA because they are against organizing such an event," the source said.
On March 16, Ging escaped unscathed when gunmen fired on his convoy just after it crossed into the unruly territory from Israel.
UNRWA, the largest U.N. agency with more than 25,000 employees, was founded after the 1948 Arab-Israeli war to provide relief for Palestinian refugees uprooted by the war.
Today the agency provides education, health, relief and social services to more than 4.3 million Palestinian refugees registered in Jordan, Lebanon, Syria, the West Bank and the Gaza Strip.
In the Gaza Strip alone, UNRWA cares for nearly one million refugees.(AFP-Naharnet)
Beirut, 06 May 07, 15:14