KABUL — U.S. troops are pulling out of Afghanistan's perilous Korengal Valley as part of a new focus on protecting population centers, NATO said Wednesday, ending a mission that saw some of the most intense fighting of the nearly nine-year American presence in the country.

The isolated mountainous region of caves and canyons on the eastern border with Pakistan has been the scene of near daily exchanges of fire between NATO and insurgents, who use it as a route for infiltrating weapons and fighters into Afghanistan.

While militants will likely portray the withdrawal as a defeat for foreign forces in Afghanistan, NATO termed the move a "realignment" resulting from changing strategies to deal with a Taliban-led insurgency that has strengthened and gripped once stable parts of the country.

The shift reflects new thinking among commanders that forces are best used to protect the civilian population rather than placed in scattered outposts highly exposed to militant activity and difficult to resupply and reinforce.

"This repositioning, in partnership with the Afghan National Security Forces, responds to the requirements of the new population-centric counterinsurgency strategy," Lt. Gen. David M. Rodriguez, joint commander of international forces in Afghanistan, said in a statement e-mailed to media. "The move does not prevent forces from rapidly responding, as necessary, to crises there in Korengal and in other parts of the region, as well."

The strategic shift coincides with the deployment of an additional 30,000 troops to Afghanistan, most on missions to drive the Taliban from populated areas and provide enough security to allow local governments to consolidate control and bring about economic recovery.

U.S. troops tested the new approach following a major offensive in February in the Marjah region of Helmand province, with mixed results so far because of lingering Taliban influence. The strategy is also expected to be a linchpin of a long-expected drive into the Taliban's spiritual homeland of Kandahar, where tribal elders have so far been largely resistant to arguments as to why they should back the central government.

Korengal, in eastern Kunar province, has a reputation as one of most dangerous areas in the country, with a rugged mountainous terrain that makes it a perfect insurgent hunting ground. Three Navy SEALs were killed in an ambush there in 2005, while a helicopter carrying special forces sent to rescue them was shot down, killing 16 American troops in one of the deadliest single attacks on the U.S. military since the war began in 2001.

Since then, insurgents have used the cover of caves and trees to attack small American units patrolling the valley, a hotbed of Taliban support whose native tribes speak a distinct language — Korengali — and adhere to the austere Wahabi brand of Islam most prevalent in Saudi Arabia, and practiced by Usama bin Laden and the Taliban. The area's 4,500 residents have long been hostile to central authority and outsiders, even those from other parts of Afghanistan.

The pullout, conducted by helicopter and carried out in secret over the past week, frees up about 120 soldiers who had been largely confined to hilltop battlements consisting of plywood, sandbags and stones.

There was no immediate word on where they would be reassigned to. Officers said one base at the northern end of the 6-mile (10 kilometer)-long valley would remain staffed to block insurgent movements into the Afghan interior.

Taliban spokesmen could not immediately be reached for comment.

Deaths of U.S. troops in other remote corners of the country have also driven the push to reassign troops to population centers, with eight Americans killed in an Oct. 3 gunbattle that broke out when hundreds of insurgents stormed a base in mountainous Nuristan province just north of Kunar. In 2008, U.S. and Afghan troops abandoned a remote outpost elsewhere in Nuristan after militants killed nine American soldiers in an assault.

Also Wednesday, an elderly tribal leader in volatile Helmand province was killed in what a local government official called an attempt by insurgents to damage traditional social structures. Lal Mohammad Khan was shot while praying in a mosque, said Abdul Ahad Khan, spokesman for the Gereshk district government.

Elsewhere, Afghan officials said a policeman died in a gunbattle and a 12-year-old boy was killed by a roadside bomb in a violent area of eastern Afghanistan.

Sayed Ismail Jahangir, spokesman for the governor of Ghazni province, said militants fired on Afghan police patrolling in Gelan district Tuesday night. Police chased a vehicle filled with insurgents to an area where more militants were lying in wait. The policeman and an insurgent were killed in a one-hour battle that followed.

The governor's spokesman said the boy died last night in Ghazni's Andar district when he stumbled onto the roadside bomb on his way home.