GAZA CITY, Gaza Strip - Israel will try to kill the entire leadership of Hamas without waiting for another attack by the militant group, security sources said Tuesday, citing a decision made by Israeli security chiefs following the assassination of Hamas� founder Sheik Ahmed Yassin. Israel's army chief also suggested that Palestinian leader Yasser Arafat and Hezbollah chief Hassan Nasrallah would eventually be assassinated.

The killing of Yassin on Monday threatened to escalate three and a half years of Israel-Palestinian fighting. Fearing revenge attacks, Israel beefed up security throughout the country and at its missions abroad.

Hundreds of thousands of Palestinians thronged the streets of Gaza City for Yassin�s funeral procession Monday, and Hamas threatened punishing revenge attacks against Israel. It also hinted for the first time that the United States could become a target for backing Israel.

Hamas, founded by Yassin in 1987, wants to destroy Israel and replace it with an Islamic state. Defense Minister Shaul Mofaz said Monday that Hamas killed 377 Israelis and wounded more than 2,000 in hundreds of attacks.

Despite the outpouring of rage, Israeli security chiefs decided during a five-hour meeting Monday to step up targeted attacks, the security sources said, speaking on condition of anonymity. They said officials decided to go after the entire Hamas leadership, without waiting for another attack by the militant group.

A decision in principle on targeting top Hamas officials was first made last week by Israel�s Cabinet, in response to a double suicide bombing on an Israeli seaport. In Monday night�s session, the security chiefs reaffirmed the direction.

Arafat, Nasrallah may be next
On Tuesday, Army chief Lt. Gen. Moshe Yaalon, was asked whether Arafat and Nasrallah, who is based in Lebanon, would be next.

Yassin's death � Latest developments � Sheik's obituary � U.S. response � Imposing figure � World reaction

"I think that their (Arafat's and Nasrallah's) responses yesterday show that they understand that it is nearing them," Yaalon said.

"In the long term, I hope that this will be a sign to all those who choose to hurt us that this will be their end," Yaalon said.

Arafat's aides said Monday the Palestinian leader was concerned he could now be in Israel's crosshairs. Israel's Cabinet decided last year that Arafat should be "removed," but never said whether this meant killing him and never acted on the decision. 

It was not clear what response by Nasrallah the army chief was referring to.

Late Monday, Hamas� leaders appeared in public at a mass mourning ceremony at Gaza�s Yarmouk stadium, apparently believing that they were safe in such a public setting. Hamas leaders often hide underground when tensions are high with Israel.

Qureia in Gaza
Palestinian Prime Minister Ahmed Qureia headed to Gaza on Tuesday to pay his condolences to Hamas. He was to attend a ceremony at the stadium later in the day.

The Palestinian Authority declared three days of mourning and stores throughout the West Bank and Gaza Strip were closed Tuesday. Hamas is the biggest rival to the authority, but Palestinian leaders treat the movement with respect because of its popularity.

Security chiefs are closely watching to see who fills the political vacuum caused by Yassin�s death.

At least initially, hardliner Abdel Aziz Rantisi, has emerged as a Hamas strongman. Rantisi, a 54-year-old pediatrician who escaped an Israeli assassination attempt last June, opposes even a temporary truce with Israel.

Hints that U.S. could be targeted
The assassination of Yassin was part of Prime Minister Ariel Sharon�s effort to crush Hamas ahead of Israel�s possible withdrawal from Gaza. However, the killing was seen as an enormous gamble that could galvanize the Palestinians behind Hamas. Rival Palestinian militant groups immediately pledged solidarity with Hamas.

The missile strike dealt what could be the final blow to the stalled U.S.-led �road map� peace plan. It also angered Egypt and Jordan, moderate Arab states whose tacit support Sharon needs for any unilateral withdrawal from Gaza.

For the first time, Hamas also threatened the United States, saying its backing of Israel made the assassination possible.

�The Zionists didn�t carry out their operation without getting the consent of the terrorist American administration and it [the United States] must take responsibility for this crime,� Hamas said in a statement. �All the Muslims of the world will be honored to join in on the retaliation for this crime.�

Homeland Security Secretary Tom Ridge was heeding the Hamas terror warning.

�If they are threatening the United States, we have to take it quite seriously,� he told reporters in Washington.

In the past, Hamas leaders have insisted that their struggle is against Israel and that they would not get involved in causes by militant Muslims in other parts of the world. Monday�s statement suggested that Hamas might seek outside help in carrying out revenge attacks, since its capabilities have been limited by Israeli military strikes.

The al-Aqsa Martyrs Brigades, which is part of the Fatah faction of Palestinian Authority President Yasser Arafat and, like Hamas, is responsible for past suicide bombings, called for �war, war, war on the sons of Zion. An eye for an eye. There will be a response within hours, God willing.�

Israel beefs up security
Fearing a revenge attack, Israel has increased security both at home and abroad. Jerusalem�s usually lively streets were mostly empty Monday night, due to fears of a Hamas attack. Buses remained empty on Tuesday.

Checkpoints were set up around major cities, and police were visible on city streets Tuesday. Tel Aviv police commander Yossi Sedbon told Army Radio on Tuesday that he expects the alert level to remain high for at least a month.

A closure preventing Palestinians from entering Israel from the West Bank and Gaza remained in effect, and the army increased forces throughout the Palestinian areas, officials said. Five Palestinians died in violence following Yassin�s killing Monday; only minor stone-throwing clashes in the West Bank were reported Tuesday.

Troops were prepared for a variety of scenarios, including kidnappings and attacks on army bases and Jewish settlements in the West Bank and Gaza, the officials said. Security also was beefed up for military and political leaders.

Forces increased security along the northern border with Lebanon in fear of a Hezbollah attack. The Lebanese guerrilla group fired anti-tank missiles and artillery rounds at Israeli troops late Monday, drawing Israeli return fire. No casualties were reported.

Outside the country, Israel stepped up security at embassies, consulates and other official offices. Israeli officials also advised various Jewish centers around the world to take precautions.

Poll shows Israeli support for assassination
The assassination, which killed seven other people, received large support in Israel, despite the belief that it will spark more violence. The Yediot Ahronot daily published a poll showing 60 percent of Israelis that killing Yassin was the right thing to do, while 32 percent thought it was wrong.

On the other hand, 81 percent of Israelis believe the assassination will lead to an increase in militant attacks, while 15 percent think it will have no impact and only three percent think it will lead to a decrease. The Dahaf poll had a margin of error of 4.4 percentage points.

�No one in the system, not even Sharon, believes that the assassination of the sheik will reduce the scope of terror. There is no strategy here: just bitter frustration and mounting difficulty to look the voters in the eye,� wrote Yediot columnist Nahum Barnea.

Israeli media reported Tuesday that Avi Dichter, the director of Israel�s Shin Bet internal security service, had opposed Monday�s airstrike.

The Maariv daily said Dichter favors waiting for Hamas leaders to gather together and killing them in one blow. It said he is concerned about revenge attacks each time a Hamas leader is targeted.

U.S. urges restraint; U.N., EU condemn attack
The United States, Israel�s closest ally, said it was �deeply troubled� by the assassination and urged restraint. U.S. officials were also quick to deny suggestions by Hamas that Israel had Washington�s approval for the assassination or had at least provided warning.

The United Nations and the European Union � which along with the United States and Russia formed the �quartet� that agreed on the �road map� to a Palestinian state � condemned the killing, which also sparked fury across the Arab and wider Islamic world.

�Such actions are not only contrary to international law, but they do not do anything to help the search for a peaceful solution,� U.N. Secretary General Kofi Annan said.

A team of top Israeli officials, including Sharon�s bureau chief Dov Weisglass and National Security chief Giora Eiland, were headed to Washington on Tuesday to discuss the withdrawal plan with American officials.