NABLUS, West Bank — Dozens of Israeli jeeps and armored vehicles poured into Nablus overnight yesterday, placing large areas of the city under curfew and conducting house-to-house arrest raids in one of the largest West Bank military operations in months.

The army also took over local television and radio stations, ordering people to remain indoors and warning residents that the clampdown would remain in effect for several days, Palestinian Arab residents said. Two soldiers and several Palestinian Arabs were lightly wounded in clashes, officials said.

An Israeli military spokesman said the operation was aimed at countering “terrorist threats” in Nablus. The raid came a day after Israeli troops discovered an explosives laboratory in the city. Nablus, the West Bank’s largest city and commercial center, is known as a stronghold of Palestinian Arab militants.

Palestinian Arab officials condemned the raid, saying it threatened President Abbas’s efforts to restart peace talks with Israel.

Mr. Abbas held a rare meeting last week with Israel’s Prime Minister Olmert and Secretary of State Rice. Although little progress was made at the meeting, participants said they discussed the possibility of extending a cease-fire in the Gaza Strip to the West Bank.

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

The Israeli forces began moving into Nablus about 3 a.m. and continued to move in for several hours, Palestinian Arab witnesses said. They said about 80 military vehicles, along with several bulldozers, were in the city.

The bulldozers erected huge piles of rubble to block movement on main roads, witnesses said. The main entrance to the city also was closed.

The operation was focused on Nablus’s 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.

Soldiers moved from door to door, entering homes in search of suspects.

At one point, nervous soldiers forced a Palestinian Arab youth to lead a small group of soldiers up some stairs and into a home ahead of the forces. The soldiers then took the youth, along with several young Palestinian Arab men, into a military vehicle. A group of young boys peeked out from the window of a neighboring building.

Israel’s Supreme Court in 2005 banned the practice of using Palestinian Arab civilians as “human shields,” though the army challenged the decision. The army had no immediate comment on yesterday’s incident, which was filmed by AP Television News.

While the operation largely shut down Nablus, sporadic clashes were reported. Soldiers were pelted with stones and cement blocks, and they exchanged fire with Palestinian Arab gunmen, the army said, adding that two soldiers were lightly wounded by a bomb.

The army responded to the protests with rubber bullets and stun grenades, witnesses said. In one incident, soldiers entered a cemetery to search for Palestinian Arabs who had pelted their vehicle with stones.