Israel Defense Forces soldiers withdrew from Nablus on Saturday evening, ending a three-day hunt for militants in which dozens of Palestinians were wounded and 20 arrested.

In the course of the operation, the IDF discovered a large weapons lab that contained shrapnel pellets, explosive substances, and explosive belt, and other bomb-making material. The lab was destroyed in a controlled manner by IDF sappers.

The Palestinian sources said that the troops primarily operated in the Old City of Nablus, where schools were closed on Saturday and male residents were forbidden from leaving.

Six Palestinians were arrested on Saturday, and a total of 20 were detained since the raid began early Thursday, mostly from Fatah.

The wanted men were transferred to the Shin Bet security service for questioning in order to determine the level of their involvement in terrorism.

The most senior militant detained was Fatah member Ra'ad Ratrut, who was arrested Thursday evening along with his deputy. Two guns were found in his possession.

An IDF officer said the operation was conducted in coordination with the Palestinian Authority, in order to avoid friction with PA security forces operating in the city.

The PA told its security officers, who were recently deployed in the city in a bid backed by Israel to build up Palestinian President Mahmoud Abbas' forces, not to walk the streets in uniform or with weapons.

The raids began early Thursday when hundreds of IDF troops flooded Nablus, conducting house-to-house searches in what the army considers to be the terror capital of teh West Bank.

The move triggered a confrontation with stone-throwing youths in which at least 24 people were lightly injured.

Troops discovered Thursday evening two rockets that were in the process of being assembled. The rockets, which resemble the Qassam rocket that has plagued communities along the Gaza Strip for years, already had fins and rods that were apparently intended to function as a launcher.

According to the army, the Civil Administration is assisting the Palestinian civilian population by distributing food and medicine, as well as repairing essential infrastructure damaged in the fighting.

A senior Palestinian source told Al-Ayam, a Palestinian paper, that Israel launched the raid in order to evade its obligations under the road map for peace, by insisting that the Palestinians are not doing enough to stop terror. The sources said the move was designed to deflect criticism from U.S. President George W. Bush, who is set to arrive in the region on Wednesday.

Palestinian PM lambasts Israel over West Bank arrest raids

Palestinian Prime Minister Salam Fayyad criticized Israel on Friday for mounting a major military sweep in Nablus, saying such intervention was ruining a Western-backed internal Palestinian security plan.

"These operations destroy our efforts in the field of security, which started bearing fruits lately in a way that people felt the change," Fayyad said in a statement.

The exercise constituted the biggest since Palestinian police were deployed in the West Bank city as part of a bid by President Mahmoud Abbas to build diplomatic ties with Israel by showing he can rein in militants.

Fayyad masterminded the security plan with Western help after the Abbas government lost control of Gaza to Islamist Hamas in June. He said Israel's actions in Nablus and elsewhere had "a tremendous negative impact on efforts being exerted, including at international level, to revive the peace process."

The rebuke looked likely to add to a mood of recrimination which has muddied Israeli-Palestinian peace talks relaunched at an international conference in Annapolis, Marlyland in November.

U.S. President George W. Bush is due to visit the region next week to discuss the points of dispute with Abbas and Prime Minister Ehud Olmert.

Olmert said on Sunday there would be no easing of Israel's security measures in the West Bank, which include hundreds of roadblocks that impede Palestinian movement, until Abbas's forces prove effective against militants.

Palestinian authorities say the deployment of their police in Nablus and two other West Bank cities, Tul Karm and Bethlehem, has brought calm, with suspects arrested and weapons seized.

Two off-duty IDF soldiers were killed in a West Bank ambush last week which Olmert's office blamed on members of Abbas's security services. The Palestinians denied that charge and said they had made two arrests.