JENIN, West Bank ? Palestinian militants ambushed Israeli soldiers during intense fighting in a refugee camp Tuesday, opening fire from rooftops and setting off explosions that collapsed a building on troops in a narrow alley, the Israeli military said. Thirteen Israeli soldiers were killed and nine were wounded.

The attack in Jenin refugee camp, where the military has besieged dozens of Palestinian gunmen for the past week, was the single deadliest incident involving Israeli forces in the past 18 months of violence.

Hours after the ambush, Israeli Prime Minister Ariel Sharon said in a nationally broadcast address that the incursion into the West Bank would continue until Palestinian militias are crushed  despite U.S. pressure that he halt the 12-day-old offensive.

“It was a tough campaign, a campaign that we are continuing … until we will fulfill the decision of the Cabinet that calls for the destruction of the infrastructure of the terror groups,” Sharon said.

Earlier Tuesday, Israel pulled out of the West Bank towns of Qalqiliya and Tulkarem, raising expectations that it would end the offensive altogether and also leave Nablus, Bethlehem, Jenin and Ramallah.

Secretary of State Colin Powell, due to arrive in Israel late Thursday in an effort to work out a truce, praised the withdrawal and said he would meet with Palestinian leader Yasser Arafat during his visit.

The Israeli military confirmed 13 soldiers were killed and nine wounded in the Jenin camp  bringing to 25 the number of soldiers killed since Israel launched its offensive after a string of suicide attacks. Palestinian medics have confirmed at least 124 Palestinians killed in the campaign, but the toll was expected to rise amid reports of dead Palestinians still not evacuated from areas of battle.

An Israeli army officer died in Nablus on Tuesday, the military said, adding that he might have been killed by errant Israeli gunfire.

The Jenin camp has seen the heaviest fighting of the offensive. By Tuesday, several hundred gunmen had been pushed back to a small area of the cramped, crowded camp, with Israeli helicopter gunships providing heavy cover fire for ground troops, witnesses said.

Army spokesman Brig. Gen. Ron Kitrey said Israeli troops were ambushed in two places in the camp several yards apart. In one attack, Palestinian gunmen opened fire from rooftops on soldiers below.

Nearby, a series of bombs connected by wire exploded when Israeli soldiers entered a narrow alleyway, Kitrey said. The blast brought down part of a nearby building, burying three soldiers, whose bodies were later retrieved by the military. He said a suicide bomber may have set off the blasts.

The evacuation of the wounded took several hours, and Israel’s military censor prevented reporting on the incident for much of the day.

On Monday, President Bush made a sharp call for Israel to end its offensive. Hours later, Israeli troops pulled out of Qalqiliya and Tulkarem, though they maintained a tight cordon around them.

Israel also suggested it would not oppose Powell’s meeting Arafat, who has been confined in his Ramallah offices by Israeli troops. Israel had initially said it would keep Arafat isolated, but Israeli Cabinet Minister Gideon Saar, meanwhile, said meeting Arafat “is an American decision. That is not an Israeli decision.” Israel eased Arafat’s isolation Tuesday, allowing him to meet four senior advisers ahead of Powell’s mission.

In Cairo on Tuesday, Powell said he would try to work out a cease-fire and a resumption of political talks. He also said the United States is prepared to send U.S. observers to the region to help monitor enforcement of a truce.

In Bethlehem, Israel’s siege of the Church of the Nativity, where more than 200 armed Palestinians are holed up, entered its second week, with no sign of a resolution. Israeli tanks ringed the church Tuesday, including one parked on Manger Square, and dozens of troops manned rooftop lookouts.

In Nablus, the West Bank’s largest city, there were scattered exchanges of fire as troops took control of the densely populated downtown area, or casbah, after several days of fierce resistance by Palestinian gunmen. At least 41 Palestinians have been killed there in the fighting, but the toll was not final because some bodies were still lying in the streets, medics said.

Gilles Jacquier, a cameraman for France 2 television, was shot and wounded in the collarbone as he stepped out of his car at the entrance to el-Ain refugee camp near Nablus. He could not identify who shot him.

In Jenin, Palestinian gunmen in the camp vowed to keep fighting, residents said. Jamal Abdel Salam, an activist for the militant Hamas group who lives in the camp said the fighters told him “they prefer death to surrender. They asked me to look after their families.”

Estimates by both sides said more than 100 Palestinians have died in Jenin. An exact count was not possible because Israel barred reporters and medics from the camp.

The Association for Civil Rights in Israel said dozens of bodies were piled in the streets of the camp and residents were prevented from getting food and water. In a complaint to the Defense Ministry, the Israeli organization said the military has committed serious human rights violations in the camp, including the demolition of homes with residents still inside. “Those who left their houses to try to get supplies were shot at by the army,” the organization wrote.

There was no immediate response from the Defense Ministry.

Israeli tanks and armor drove briefly into Hebron, one of two major West Bank towns not targeted in the Israeli offensive, but then withdrew.

Israeli forces also raided the town of Dura, south of Hebron, leveling two Palestinian intelligence and security compounds. Two Palestinians were killed in exchanges of fire with Israeli forces, Palestinian security officials said.

More than 1,500 Palestinians have been arrested by Israel in the offensive, among them 70 to 80 involved in planning attacks on Israelis, Israeli military officials said.