Israeli troops withdrew Monday from areas in volatile Hebron as part of truce efforts, and an Islamic militant was killed in another West Bank town in an explosion blamed on Israel.

The victim, Ahmed Marshoud, was a member of the Islamic militant group Hamas in the town of Nablus. On Sunday, Israel killed a regional Hamas leader, saying it targeted him because he helped plot a June suicide bombing that killed 22 people.

Palestinian officials said Israel was behind Monday's explosion, while the Israeli army had no immediate comment.

"It's clear that there are parties that are looking to destroy all the international efforts aimed at stopping Israeli aggression," said Jibril Rajoub, the Palestinian security chief in the West Bank.

Also Monday, Jewish settlers opened fire on Palestinian farmers, and torched two of their cars near a West Bank village, Palestinian security officials said. There were no reports of injuries.

Israeli troops, backed by tanks, had seized two hilltop neighborhoods in Hebron on Oct. 5, after Palestinian gunmen repeatedly fired from there at Jewish settler enclaves in the center of town. Troops withdrew early Monday.

Jewish settlers entered the two neighborhoods to try to prevent the army pullback. Twenty-three settlers were detained by Israeli police, some on suspicion of assaulting soldiers, police said.

By daylight, Palestinian security forces entered the two neighborhoods, setting up checkpoints, patrolling in jeeps and taking over positions from which gunmen had fired at the settler compounds in the past, witnesses said.

Protesting the pullback, Israel's ultranationalist National Union party, a patron of the settlement movement, announced it would leave Prime Minister Ariel Sharon's coalition government.

The party has seven seats, and their exit reduces the number of seats in Sharon's coalition to 78 in the 120-member parliament. While Sharon still has a solid majority, he might now become more dependent on the moderate Labor party to stay in power.

The Hebron pullback was the result of truce talks held Sunday. Israel also agreed to ease some of its stifling travel restrictions in the West Bank.

Israeli soldiers abandoned a roadblock at the entrance to Jericho, and soldiers made it less difficult for Palestinians to pass other West Bank checkpoints.

But Jaroub, the West Bank security chief, said the Palestinians were demanding the complete lifting of the closure, which would allow Palestinians to return to Israel, where many had jobs before the violence broke out a year ago.

"It's a mistake to say that we have reached an agreement with Israel," said Rajoub. "The Israelis have proposed only some small steps to ease the closure."

The United States has been urging both sides to show restraint as it tries to build support in Arab and Muslim countries for an anti-terror campaign.

The truce has been sorely tested on both sides since it was declared Sept 26.

On Sunday, Israeli forces shot and killed Abdel-Rahman Hamad, a regional leader of Hamas living in the town of Qalqiliya.

Sharon, citing Israel's right to defend itself, said Sunday that the shooting "was not the first nor the last."

The shooting of Hamad marked a return to Israel's policy of targeted killings. Over the past year, Israel has carried out dozens of such attacks against Palestinian militants suspected of violence against Israelis.

Sunday's shooting was the first targeted killing since the cease-fire was declared.

In Nablus, Monday's explosion went off in a car parked outside an office building that is in view of an Israeli position on a nearby hilltop. The Israeli army had no immediate comment, though Israel army radio said the blast was set off by Israel.

The Palestinian governor of Nablus, Mahmoud Aloul, said Israel was behind the explosion, and that the killing was intended to sabotage truce efforts.

Hamas has carried out multiple suicide bombings against Israel, including the disco bombing, the deadliest single attack in the current round of Mideast fighting.

Palestinian leader Yasser Arafat arrived in London to meet Prime Minister Tony Blair and Foreign Secretary Jack Straw on Monday.

Britain is pressing Israel and the Palestinian Authority to be more active in seeking a peaceful resolution of their conflict, which has been a breeding ground of terror, Straw said.