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Palestinian Prime Minister Mahmoud Abbas (search) threatened to quit as premier and resigned from a key body of Yasser Arafat's Fatah movement Tuesday, reflecting turmoil within the Palestinian leadership over negotiations with Israel.

The move came just hours after Islamic militants claimed responsibility for a homicide bombing that left an elderly Israeli woman dead, and threatened more attacks unless Israel agreed to release the thousands of Palestinian prisoners that it holds.

But the chief of Israeli military intelligence, Maj. Gen. Aharon Zeevi-Farkash (search), told Israel TV on Tuesday that Israel must not release prisoners tied to terrorism. "It is forbidden to free terrorists with blood on their hands," he said.

Abbas has been facing strong pressure within his Fatah (search) movement to adopt a tough line on the prisoner releases. In a letter to Arafat, he said he would step down as premier unless he gets clear instructions from Fatah over how to handle contacts with Israel.

Fatah officials said Abbas' move might be a pressure tactic aimed at forcing Fatah members to give him greater flexibility in the talks.

Abbas' leadership is strongly backed by the United States, which rallied to his support. "We stand behind Prime Minister Abbas," State Department spokesman Philip T. Reeker said. He said Abbas' leadership has produced important changes beneficial to the Palestinians.

The Bush administration sees Abbas as a moderate alternative to Arafat (search), who is accused of involvement in terrorism.

Palestinian leaders proposed Monday that Abbas and security chief Mohammed Dahlan meet with Israeli Knesset members to help press Palestinian demands for a prisoner release. The meeting has yet to be scheduled.

Israel holds an estimated 7,000 Palestinian prisoners — an issue that threatens to become a major crisis between the sides — and this week Sharon's Cabinet decided to free perhaps 5 percent of them. Israel thought the planned prisoner release would strengthen Abbas' position. But top Palestinian officials say its limited scope could weaken Abbas by making him look ineffectual.

Arafat reluctantly appointed Abbas to the new post of Palestinian prime minister in April, giving in to intense international pressure to share power. Since then, Arafat has tried to retain as much authority as possible.

Hakam Balaawi, a Fatah official, said Abbas quit the Fatah Central Committee. Fatah, headed by Yasser Arafat, has been in turmoil over the declaration of a unilateral cease-fire — which also obligates its affiliated militia, the Al Aqsa Martyrs' Brigades — 10 days ago.

Fatah officials were trying to persuade Abbas, also known as Abu Mazen, to withdraw his resignation.

"I hope that Abu Mazen will change his mind and withdraw his resignation soon," Balaawi said.

Abbas has been Arafat's deputy in Fatah, the largest Palestinian movement, for decades.

The suicide bombing, which killed a 65-year-old woman Monday while she watched television inside her home in central Israel, was a violation of the cease-fire that began last Sunday. The attack may have been carried out by a splinter group within the militant Islamic Jihad organization.

The militants who claimed Monday night's bombing said it was carried out to press demands for a sweeping prisoner release.

The Hamas and Islamic Jihad groups are seething over the plans because Israel has explicitly ruled out freeing any of their members. Slightly fewer than half of the detainees are members of Islamic Jihad or Hamas, according to Radi Jarrai, deputy minister for prisoner affairs in the Palestinian Authority,

A videotape of the bomber, 22-year-old Ahmed Yehyia, circulating in the northern West Bank town of Jenin (search), showed a young man in blue jeans and a T-shirt holding a Kalashnikov assault rifle.

"I carried out this operation as a gift to the prisoners in the Zionist prisons," Yehyia said, identifying himself as a member of the military wing of Islamic Jihad.

Islamic Jihad's political leader in the West Bank, Sheik Bassam Saadi, stressed that the group "is committed to the (truce) and it remains so today." He said Jenin-based militants probably staged Monday's attack as a reaction to Israel's decision not to release prisoners affiliated with the group.

Israeli Defense Minister Shaul Mofaz said Tuesday that Israel would continue with peace efforts but had to protect its citizens. "We will continue operating against this infrastructure," he said, referring to Islamic Jihad.

The bombing is the first since Palestinian militants declared a cease-fire on June 29; the last Palestinian homicide bombing killed 17 people on a bus in Jerusalem on June 11.

Israeli Foreign Minister Silvan Shalom said peace efforts would continue despite the bombing. "We have an opportunity now that we must not miss, which we have to check out thoroughly and see if it is really genuine," he told Israeli army radio.

The issue of prisoner releases also is deeply emotional for Israelis.

Many Israelis believe that the mass arrests of militants were key to slowing down the spate of homicide bombings that left hundreds dead. There is also the widespread belief that past prisoner releases led to an upsurge in violence.

The issue, in any case, is not part of the U.S.-backed "road map" peace plan; but the blueprint does mention an earlier, failed U.S. truce plan that called for Israel to free Palestinians "who have no association with terrorist activities."

In the most recent truce, Hamas and Islamic Jihad promised to halt attacks against Israel for three months and a militia associated with Yasser Arafat's Fatah vowed to halt attacks for six months.

Israel responded by pulling out of parts of Gaza and the West Bank town of Bethlehem, and has promised further withdrawals — if the Palestinians move to disarm the militant groups. Abbas has said he will accomplish this by persuasion, but will not use force.