NABLUS, West Bank (AP) – Israeli soldiers sealed off this city on Sunday, placed much of it under curfew and conducted house-to-house searches for Palestinian Arab militants in the largest military operation in the West Bank in months.

Israeli officials said the wide-scale raid was crucial to stopping future militant attacks against Israel, but Palestinian officials said the offensive threatened nascent efforts to restart the peace process. The raid began early Sunday morning, when about 80 jeeps, armored vehicles and bulldozers poured into Nablus, which is known as a hotbed of militancy, witnesses said. Soldiers closed the main entrance to the city and bulldozers erected huge piles of rubble to block off key roads.

The operation was focused on Nablus’ Old City, or casbah, a densely populated area of narrow alleyways, apartment buildings and markets. About 50,000 people were placed under curfew, residents said.

The military took over local TV and radio stations and ordered people to remain indoors, warning the clampdown would remain in effect for several days, residents said. The army said the road closures and curfew were necessary to avoid civilian casualties.

Soldiers then moved from house to house in search of suspects. At one point, a small group forced a Palestinian youth to lead them into a home. Afterward, the soldiers placed him, along with several young Palestinian men, into a military vehicle.

Israel’s Supreme Court in 2005 banned the practice of using Palestinian civilians as “human shields” to search homes for explosives or militants ahead of soldiers. The army had no immediate comment on Sunday’s incident, which was filmed by AP Television News.

Sporadic clashes were reported as soldiers were pelted with stones and cement blocks and exchanged fire with Palestinian gunmen, the army said. The army responded with rubber bullets and stun grenades, witnesses said. In one incident, soldiers entered a cemetery to search for Palestinians who had pelted their vehicle with stones.

The army said two soldiers were slightly wounded by a Palestinian bomb; Palestinian medical officials said four Palestinians were wounded by rubber bullets.

The raid came a day after Israeli troops discovered an explosives lab in the city, the West Bank’s commercial center. Maj.]or Avital Leibovich, an army spokeswoman, said troops uncovered another explosives lab and small caches of weapons on Sunday.

The open-ended operation was intended to “to deal with Nablus as a terror hub, with minimum of hurting or injuring innocent civilians,” she said. “We cannot allow the explosives of these labs to be turned against our civilians, our children, our malls, restaurants.”

Palestinian officials said the raid threatened new peace efforts.

Mr. Abbas met last week with Israeli Prime Minister Ehud Olmert and Secretary of State Rice in Jerusalem. Though the meeting yielded little progress, participants said they discussed the possibility of extending an Israeli-Palestinian cease-fire in the Gaza Strip to the West Bank.

The raid came at a sensitive time for the moderate Abbas, who is trying to cobble together a unity government with the radical Hamas group.

Hamas and Mr. Abbas’ Fatah party reached a power-sharing deal earlier this month in Saudi Arabia, which Mr. Abbas had hoped would pave the way for ending international sanctions imposed on the current Hamas-led government. Palestinian officials said Sunday the economy contracted 21 percent in the fourth quarter because of the boycott.

Israel and Western donor nations, however, have warned they will not lift the sanctions if the new government does not agree to renounce violence and recognize Israel’s right to exist. The unity accord pledges only to “respect” past agreements.

Ghazi Hamad, spokesman for the Hamas-led government, said the Nablus raid was part of an Israeli effort to destroy the unity deal.

Also Sunday, a smugglers’ tunnel under the Gaza-Egypt border collapsed, injuring three people. Security officials said it belonged to a clan known for drugs and weapons dealing. Israel says the Palestinians have smuggled in a steady stream of weapons from Egypt since Israel pulled out of Gaza in 2005.