Israel renewed its blockade of several West Bank cities Thursday in response to a spate of killings of Israelis by Palestinian militants this week and warnings that more attacks were being planned.

Also Thursday, a local Palestinian militia leader wanted by Israel was killed in an exchange of fire with Israeli troops, the Israeli military said.

In the West Bank town of Ramallah, a radical PLO faction protesting the detention of its leader by Palestinian police threatened to attack senior Palestinian security officials if more arrests were made.

"We will get to [the security officials], regardless of how many guards they surround themselves with," the military wing of the Popular Front for the Liberation of Palestine (PFLP) said in a leaflet.

The violence and new Israeli blockades represent a further deterioration of an informal cease-fire and easing of restrictions that followed Palestinian leader Yasser Arafat's Dec. 16 declaration that he would enforce a truce with Israel.

Israel's security Cabinet met until 3 a.m. Thursday and approved a decision by Defense Minister Binyamin Ben-Eliezer to seal the West Bank cities of Qalqilya, Jenin, Tulkarem and Nablus.

Palestinians said Israel also closed Bethlehem, barring Palestinians from entering or leaving. The army said Bethlehem was not sealed.

Israel has enforced stringent travel bans on Palestinians since the outbreak of fighting in September 2000. For much of this time, Palestinians have been barred from leaving their communities, which are ringed by Israeli roadblocks. Israel says the restrictions are necessary to keep suspected militants out of Israel.

The restrictions were eased slightly after Arafat's truce announcement.

The blockades were renewed after three civilians -- an American man, an Israeli woman and a Palestinian resident of Jerusalem -- were killed in Palestinian shooting attacks this week.

The Palestinian gunman killed Thursday was identified as Khamis Abdullah, 42, head of a militia linked to Arafat's Fatah movement in the Askar refugee camp near Nablus. Palestinian officials said Abdullah and other members of his group opened fire early Thursday on Israeli tanks deployed near Nablus, drawing return fire that killed him.

The Israeli military said Abdullah was alone and was spotted by Israeli troops who opened fire. He returned fire, but was hit, the military said.

Israeli security sources said Abdullah was killed by an Israeli commando force, not soldiers on a routine patrol.

Ben-Eliezer warned Palestinian militants not to escalate the situation.

"We won't give up on our elementary right to defend our homes, defend our children, and defend our families," he told Israel Army Radio.

Palestinian Parliament Speaker Ahmed Qureia said renewed Israeli closures would only lead to more friction.

"This is not the way to lead the situation to quiet, and I am afraid it will very dangerous in the future," Qureia said.

The Palestinian attacks came in response to the death of Palestinian militia leader Raed Karmi, who was killed in a Monday bomb blast widely attributed to Israel. Karmi's supporters have vowed to avenge their leader's death.

Arafat said after a meeting with Spanish Foreign Minister Josep Pique on Thursday that he would continue to enforce a truce.

Asked whether he expected a confrontation with the PFLP after arresting its leader, Ahmed Saadat, Arafat said: "Not just with the PFLP, but with other factions. All have to understand that there is one decision taken by the Palestinian Authority. We are doing our duty to protect the Palestinian national interests."

Arafat said he wants Saadat to turn over the assassins of Israeli Cabinet Minister Rehavam Zeevi, who was killed in October by PFLP supporters.

Israel has repeatedly accused the Palestinian Authority of not being serious about arresting militants or preventing attacks against Israelis.

Arafat said his forces had trouble finding Saadat, who lives in Ramallah, the West Bank town to which Arafat has been confined for the past few weeks by Israel.

"Only yesterday we found out where he was," Arafat said. "He had shaved his mustache and made some changes in his appearance."

Israel has said it will not let Arafat leave Ramallah until the those involved in the killing of Zeevi have been arrested and turned over to Israel.