GAZA CITY, 13 December — Palestinian gunmen killed 10 Israelis, mostly Jewish settlers, in a bus ambush in the West Bank and bombers struck a settlement in the Gaza Strip yesterday. The assaults, which wounded more than 30 people in all, were in retaliation of an Israeli helicopter raid that killed four Palestinians overnight in the Gaza Strip. Another Israeli settler was also killed when an Israeli tank exploded in Nablus.

The violence came a day after US envoy Anthony Zinni had secured an agreement by both sides to seek 48 hours of calm in an attempt to ease tensions after nearly 15 months of conflict in which nearly a thousand people have been killed.

The Israeli government said it blamed Palestinian President Yasser Arafat for not reining in hard-liners and by nightfall the now familiar Israeli helicopter raids and F-16 bombings of Palestinian areas had begun. Israeli missiles rained on Palestinian security installations in the Gaza Strip and the West Bank town of Nablus. The Palestinian Authority denied Israeli accusation of Arafat’s complicity, strongly condemned the attacks and closed down immediately all institutions belonging to the Hamas and Islamic Jihad groups.

“The Palestinian Authority in an urgent meeting headed by Arafat has taken a decision that Palestinian security forces will immediately close down all Hamas and Islamic Jihad institutions, including education, health and political offices,” an official statement said.

The Al-Aqsa Martyrs Brigade, an armed group linked to Arafat’s Fatah group, claimed responsibility for the attack on the bus. It said the attack was in retaliation for overnight killings by Israeli forces.

A roadside bomb was detonated as the bus turned a corner near the entrance to the Jewish settlement of Immanuel in the northern West Bank. Seconds later, three Palestinian gunmen tossed grenades and opened fire with machine guns at passengers fleeing the bus after the explosion. Many of the victims were settlers, whom Palestinians consider legitimate targets as occupiers of Palestinian lands.

The body of one gunman lay sprawled on the ground, still holding an M-16 automatic rifle and pistol. The bus driver had apparently run him over as he fired and then police shot him dead.

The other two gunmen fled, and Israeli soldiers conducted a manhunt in nearby hills for the gunmen firing flares to light the night sky.

Minutes after the bus attack, two bombers blew themselves up at the Gush Katif Jewish settlement bloc in the Gaza Strip. Israeli security sources and Israeli television said at least three people were wounded.

Late on Tuesday, Israeli helicopter gunships killed four Palestinians near Khan Younis refugee camp, overlooking a Jewish settlement. Palestinian officials accused Israel of assassinating members of the Abu Rish Brigades, an armed, breakaway faction of the Fatah group. They say Israel’s strikes hamper efforts by Palestinian security forces to crack down on hard-line groups.

The United States called the Palestinian attacks “horrific actions” and urged Arafat to take immediate action to apprehend those responsible. Washington was, however, silent on the Israeli assassinations that provoked the attack. “We absolutely condemn it in the strongest terms,” State Department spokesman Richard Boucher said.

Boucher urged Arafat to act quickly to stop the violence. “Once again, we stress that it is absolutely imperative that Chairman Arafat and the Palestinian Authority act immediately and undertake all possible measures to pursue and apprehend those responsible for those horrific actions.” The latest bloodshed cast further doubt on the effectiveness of Zinni’s mission, already dented by a wave of Israeli airstrikes and retaliatory Palestinian bombings. Zinni had earlier this week seemed almost ready to pack up and go home after two weeks spent in the region to the accompaniment of some of the worst violence in months.

Asked about Zinni’s plans, Boucher said the retired general intended to stay in the region for the foreseeable future as long as the parties were willing to work with him and continued to work together to achieve a cease-fire.”

In a separate news briefing, White House spokesman Ari Fleischer said Zinni remained “committed to helping the parties find a way to begin the security talks and the president remains hopeful that the talks can begin”.

UN Secretary-General Kofi Annan criticized Israel’s demand for a total suspension of violence before resuming talks with the Palestinians, saying that approach allowed hard-liners to derail efforts to make peace in the region. “The current approach of no violence, 100 percent satisfaction on cease-fire, no violence for one day, two days, seven days in a way has given a veto to almost every extremist,” Annan said in an address to the Swedish parliament.

He said peace talks needed to resume immediately with the understanding that both sides must deal harshly with those bent on violence.

In Cairo, Arab League chief Amr Moussa warned Israel that any attempt to kill President Arafat would lead to grave consequences. Moussa also called for international action to send monitors to the region to ensure the safety of civilians and to monitor breaches of peace agreements, the Egyptian news agency MENA said.

At least 760 Palestinians and 223 Israelis have been killed since the latest Palestinian uprising against Israeli occupation began in September 2000.