Nablus, West Bank ? Israeli soldiers sealed off this city Sunday, placed its densely populated center under curfew and conducted house-to-house searches for Palestinian 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.

“We condemn this military incursion,” said Saeb Erekat, aide to Palestinian President Mahmoud Abbas. “This will undermine the efforts that are being made to sustain the cease-fire with Israel.”

It was first large-scale operation in the West Bank since Israeli forces entered Nablus last July and surrounded a security compound to arrest suspected militants.

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.

Area commander Brig. Gen. Yair Golan said the offensive was necessary because of the increased militant activity in Nablus. “We entered the city to lower the threat level to Israel and hit terror infrastructure,” he said in a phone interview.

Palestinian officials said the raid threatened new peace efforts.