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Israel has decided to target top Hamas leaders, including founder Sheik Ahmed Yassin (search), Israeli officials and media said Friday, confirming a policy change likely to speed up an attack-revenge cycle that has already claimed 47 lives in four days.

The violence is jeopardizing a U.S.-backed plan, launched just last week, that calls for Mideast peace and Palestinian statehood by 2005.

Israel decided to escalate its war on Hamas (search) after the Islamic militant group last week rejected cease-fire talks, said an Israeli security official, speaking on condition of anonymity.

Hamas leaders, who had not been targeted by Israel in the past 32 months of fighting, are now marked for death, the official said. They are considered "ticking bombs" — and therefore legitimate targets — because they set policy and order attacks on Israelis, the official said.

Avi Pazner, a government spokesman, said "there is no immunity for anybody who either orders or executes terrorist activities."

And military correspondent Alex Fishman wrote in the Yediot Ahronot (search) daily Friday that "from now on, everyone is in the crosshairs all the time," including Yassin.

Raanan Gissin, an adviser to Israeli Prime Minister Ariel Sharon (search), insisted there was no policy change, but said: "We don't target political leaders, but if those leaders have politics of murder, we go after them."

Israel rejects Hamas' claim that there is a strict separation between the group's political leaders, including Yassin, and the military wing that has killed hundreds of Israelis in bombings.

During the past 32 months of fighting, Israel has killed more than 100 wanted Palestinians in targeted attacks, including many from the Hamas military wing. The group's top political leaders were left alone, possibly because of Israel's fear of a bloody backlash.

However, Israel recently developed a contingency plan for going after the top leaders. The plan was activated last week, after Hamas broke off talks with Palestinian Prime Minister Mahmoud Abbas (search) on halting attacks on Israelis, the security official and Israeli media said.

The first target was Abdel Aziz Rantisi, a Hamas co-founder and spokesman. Rantisi, a 55-year-old pediatrician, escaped an Israeli missile strike Wednesday with minor injuries, while his bodyguard and a bystander were killed.

In response, a Hamas suicide bomber killed 17 people and wounded more than 70 in a Jerusalem bus attack a day later and Hamas threatened more bombings.

Israel, in turn, carried out three more missile strikes that killed five Hamas operatives and commanders, along with 13 bystanders, in Gaza City. About 70 people were wounded in those attacks.

Hamas has ordered an all-out assault on Israelis and urged foreigners to leave Israel for their own safety. Mahmoud Zahar, a Hamas leader, accused Sharon of declaring war on Hamas. "We accept the challenge," Zahar said. "Every Israeli is a target for us."

A poll published Friday in the Yediot Ahronot newspaper showed that 58 percent of Israelis believe the military should temporarily halt the killing of militants to give Abbas a chance to establish his influence in his government. The poll surveyed 501 Israelis and has a margin of error of 4.5 percent.

Late Thursday, Palestinians shot and killed an Israeli motorist in the West Bank, and Israeli soldiers went in to the West Bank town of Jenin and killed two Islamic Jihad activists. Two more Israeli motorists were wounded Friday in a shooting attack near the town of Ramallah. Also in the West Bank, Palestinians shot and killed one Israeli and wounded two more.

Also Friday, the army blew up an apartment belonging to the family of Wednesday's suicide bomber, a 17-year-old high school student from the West Bank city of Hebron. The nearby home of another Palestinian gunman was also destroyed, a measure the military uses to punish families of attackers and to try to deter others from carrying out attacks.

With the "road map" plan leading nowhere, U.S. Secretary of State Colin Powell will meet in Jordan next week with other members of the so-called "Quartet" of Mideast mediators — the European Union, United Nations and Russia.

Powell called on Abbas to work harder to rein in militants. "We want him to use that limited capability as effectively as he can," Powell told The Associated Press in an interview after talking to Sharon and Abbas on the telephone.

In Cairo, Arab League Secretary-General Amr Moussa said U.S. observers must be sent soon. "We all have to stop the violence and the bloodshed or at least freeze the situation for sometime until things are cooled off," Moussa told reporters.

A team of American observers is to arrive next week, part of the road map plan.