Security was beefed up at the main U.N. compound in Gaza City Monday, with workers reinforcing the entrance gate and personnel inspecting the roof after a shadowy group of Muslim extremists attacked a U.N.-run school.

Sunday's incident, which killed one and wounded seven, is part of Gaza's out-of-control lawlessness that is increasingly aimed at foreigners. Most foreigners have left Gaza, and the latest attack on the U.N. was seen as a major escalation.

There was no claim of responsibility for the attack in the southern Gaza refugee camp of Rafah, but security officials said they believe "salafiyeen," or Muslim fundamentalists, were involved. The group is believed to be behind a string of attacks on Internet cafes and music shops in recent weeks. It is not clear whether they are connected to any political party.

The latest incident underscored the inability of the new Palestinian unity government, a coalition of the Islamic militant Hamas and the Fatah movement of moderate Palestinian President Mahmoud Abbas, to end the chaos.

Abbas and Prime Minister Ismail Haniyeh of Hamas met late Sunday in another attempt to put together a security plan. The meeting ended without agreement, and another was set for Monday.

Interior Minister Hani Kawasmeh, the author of the plan, has threatened to resign because security commanders refuse to cooperate, mainly because of rivalries between coalition partners Hamas and Fatah.

New statistics illustrated the sharp increase in internal violence in Gaza.

In the first three months of this year, 147 Gazans, including 10 children, were killed by fellow Palestinians, according to the Palestinian human rights group Al-Mezan. By comparison, 57 people died in factional fighting in all of 2004, followed by 101 in 2005 and 252 last year.

If the upward spiral is not stopped, Gaza could become ungovernable, warned Ibrahim Ibrach, a political scientist at Gaza's al-Azhar University. "The collapse of the Palestinian Authority ... is at stake," he said.

Sunday's attack on the U.N. school in the southern Gaza refugee camp of Rafah began with a protest by Muslim extremists in long robes, who said a sports festival the school was hosting was un-Islamic. The U.N. "is turning schools into nightclubs," read one sign held up by the protesters.

At one point, the group tried to enter the school. Palestinian security fired in the air to keep them away. In the ensuing chaos, at least one bomb was thrown into the school, and a gun battle followed.

A senior Fatah official, Majed Abu Shamaleh, was leaving the school when his bodyguard was killed. Seven people were wounded, most by bomb fragments. Some children hid under their chairs during the fighting.

Police arrested two of the gunmen and were interrogating them. Later, the extremists tried to approach the police station where the two suspects were being held, to release the men. Police and gunmen from militant factions surrounded the station to prevent the extremists from entering, witnesses said.

So-called salafiyeen are known through the Muslim world as fundamentalists who try to imitate their pious ancestors and recreate the lifestyle of Islam's founder, the Prophet Muhammad. Most are peaceful, but some engage in violence.

A Palestinian intelligence official said the Gaza group appeared determined to attack all those who don't agree with its strict ideology. Other fundamentalist groups have existed in the same area of southern Gaza for years, but live in their own communities and peacefully preach their beliefs, he said.

"What's new is that this group, which seems to have developed a few years ago, believes in violence if they see things they believe is wrong," the official said. He spoke on condition of anonymity because he was not authorized to speak to the press.

He said the group has no more than dozens of members, but could easily grow as disaffected youths abandon the two largest political groups, Hamas and Fatah.