Israeli air strikes continued for a fourth straight day on the Gaza Strip and incursions in the West Bank brought to 37 the number of Palestinians killed, as Israel imposed a lockdown on the strip, banning the movement of goods and people in and out of Gaza.

Arab television reports said two militants from Hamas' al-Qassam Brigades were killed and a third was injured in the northern Gaza Strip. The Israeli army said it targeted "a rocket-launching squad after they fired rockets into Israel."

A Palestinian woman was killed and 46 others were wounded, including children, when F-16 fighter airplanes fired missiles on the former Interior Ministry of the ousted Hamas government in Gaza City. The building was abandoned, but the bomb damaged 15 nearby houses and injured people on their way to a wedding in the neighborhood.

Israeli leaders have vowed to step up their military crackdown against Hamas and other armed groups in the Gaza Strip, saying the campaign will not cease until Palestinians stop launching home-made Qassam rockets and mortar fire on nearby Israeli towns and positions.

Five rockets landed in Israeli communities near Gaza on Friday. Militants this week fired around 150 rockets and mortar shells on Israeli targets, slightly injuring more than 10 people.

The U.N. Relief and Works Agency for Palestinian Refugees called on Israel to open the border crossings into Gaza, where movement was already restricted since the Hamas takeover last June.

But Israel's Defense Ministry indicated the closure, slapped early Friday, was temporary and depended on whether rocket fire continued.

A former chief of the Israeli army's planning department, Shlomo Brom, told AFP news agency that Israel was "pursuing a double objective -- to limit the rockets as much as possible and to weaken Hamas."

But the Israeli military operations are also targeting the West Bank, controlled by the Fatah-led Palestinian Authority of President Mahmoud Abbas.

In the West Bank refugee camp of Balata in Nablus, a local commander of the al-Aqsa Martyrs Brigades, an armed wing of Fatah, was killed Friday after a gunfight with Israeli troops who besieged a house in which he and three other gunmen were hiding. The Israeli forces imposed a curfew on the camp, but withdrew after arresting the three other gunmen, according to eye-witnesses.

Israeli troops have been raiding towns and refugee camps in the West Bank to hunt down militants, which the PA condemned as sabotaging its security plan to disarm gunmen in return for Israeli amnesty as part of the international peace Quartet's road map.

But the security plan, intended to demonstrate goodwill for peace and to show Palestinians that giving up arms would remove an Israeli excuse to attack, seemed to blow up in Abbas' face with the escalated campaign in the West Bank.

Palestinian officials complain the Israeli forces have also been arresting former Fatah gunmen who joined the PA security forces, indicating that Israel will deal with the Fatah-led PA in the West Bank in the same way it deals with Hamas-controlled Gaza.

But Abbas and his Palestinian Authority have so far resisted growing pressure to stop the negotiations with Israel, despite its heightened onslaught on Gaza and increased incursions into the West Bank since the peace talks were formally revived late November at a U.S.-sponsored Middle East conference in Annapolis, Maryland.

Yet on Friday, some Palestinian newspapers close to the Fatah leadership reported that Abbas had privately threatened to resign and withdraw from the negotiations because his authority and credibility were being undermined by the Israeli operations.

While there was no official confirmation of Abbas' threat to pull out of the talks, Palestinian observers say the leak in the mainstream Palestinian press indicated the level of pressure on Abbas from within his own Fatah movement and to send a message to ease widespread rage for continuing peace talks with ongoing Israeli assaults.

Officially, however, the Palestinian Authority wants to show it is serious about peace, saying it will continue the negotiations. It apparently has little other choice at this stage while the Jewish state sustains its attacks, even in the face of international appeals for "self-restraint."

Nabil Abu Rdeineh, Abbas' spokesman, told al-Jazeera TV Friday the Israeli attacks raise questions on whether Israel is serious about peace and what the administration of U.S. President George W. Bush is willing to do to protect its credibility as a peace broker.

Rdeineh stressed that negotiations, which he said have not produced any results yet, will continue "because we don't want to give Israel the pretext to say we don't want peace and we refuse to be pulled into marginal battles."

Analysts say the Palestinian Authority is also concerned about possibly losing $7 billion in aid pledged to the Palestinians at an international donor's conference in Paris last month, which was linked to progress in the peace talks and the PA's ability to stop attacks on Israel.

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With agency dispatches.