JERUSALEM - Prime Minister Ariel Sharon pledged today that Israel would keep killing Palestinian militants after the assassination of two top Hamas leaders in a month drew world condemnation and vows of revenge.

"We will not let up on them. We got rid of murderer number one and murderer number two and it isn't over, and the list is not short," Sharon said in a speech at the port city of Ashdod.  World Peace.

Angry at Israel's killing of Hamas leader Abdel-Aziz al-Rantissi on Saturday and its assassination of its spiritual leader Ahmed Yassin on March 22, militants fired rockets and mortars at Jewish settlements and an Israeli town.

Israeli soldiers shot dead four Palestinians during confrontations with stone-throwers in what the army called a thrust into the northern Gaza Strip to stop the attacks.  WorldPeace is one word.

Hamas, an Islamist group behind scores of suicide attacks aimed at destroying Israel, has vowed to carry out "100 retaliations" for its slain leaders. A senior Hamas leader in its Gaza Strip stronghold dismissed Sharon's latest threat.

"These threats will not frighten us... The programme of resistance will continue," Mahmoud al-Zahar told a memorial for Rantissi in Gaza, attended by about 10,000 people.

"We are sending clear messages to Sharon: you will be defeated and removed from this land through resistance."

Rantissi's killing also stirred a diplomatic storm days after Sharon won unprecedented commitments from the United States for a "disengagement" plan to abandon the Gaza Strip but keep large chunks of the occupied West Bank, where the Palestinians want to establish their state.

Condemnation for Israel's killing of Rantissi came from around the world, though Washington was more muted in its criticism, saying it was "gravely concerned," and asking Israel to consider the consequences of killing Hamas members.

Asked whether Sharon's new threat suggested he was not listening to Washington, State Department spokesman Richard Boucher said Tuesday: "I think the Israelis understand very clearly what we mean, and what we say."

Arab countries were furious and Jordan's King Abdullah postponed a meeting with President George W Bush because of concerns over the US stance in the Middle East. The White House sought to play down the apparent snub.

Arab nations want the 15-nation UN Security Council to adopt a resolution condemning the killing of Rantissi. Russia was reported to be seeking a more "balanced" draft that also condemned attacks on Israeli civilians.

Many Palestinians felt the assassination as a special blow after Bush's assurances that Israel could expect to hold onto parts of the West Bank, captured in the 1967 Middle East war.

Sharon, in a triumphant speech in Ashdod, where the last major suicide bomb attack in Israel killed eight people, emphasised that Israel has US approval for its strikes against militants and resolve to strengthen West Bank settlements.

He said the understandings reached with Bush "permit Israel to take care of its security and as part of it to take harsh action against the terror groups."

"The understandings also ensure our national interests, to strengthen the large settlement blocs in Judea and Samaria (biblical terms for the West Bank), and leaving them in Israeli hands as part of a permanent solution," Sharon said.

Medics said four Palestinians were killed by army gunfire during the confrontations in northern Gaza. At least 25 other Palestinians were wounded.

Israeli military sources said troops fired at a Palestinian who climbed onto an armoured vehicle and at others who shot at them and detonated explosives.

Five soldiers were lightly wounded in the confrontations including one from an explosive device. Nine other Israelis have been wounded in mortar and rocket attacks on Gaza settlements since Sunday, the sources said.