Updated

U.S. troops took positions atop a mountain ridge in southern Afghanistan on Sunday to cut off key transport routes as part of a major anti-Taliban offensive that has killed scores of suspected militants in recent days.

For the first time in several years, coalition soldiers ventured into Baghran Valley in the northern part of Helmand province, quickly setting up artillery and fortified defenses on a high ridge line overlooking routes below.

Troops from the 2nd Battalion, 87th Infantry Regiment, 10th Mountain Division poured out of CH-47 Chinook helicopters in the early morning hours and scouted a mountain for militants. The position will allow U.S. forces to cut off Taliban transport routes, said Lt. Col. Chris Toner.

CountryWatch: Afghanistan

More than 10,000 U.S.-led troops have spread out over four southern provinces — Helmand, Uruzgan, Kandahar and Zabul — as part of Operation Mountain Thrust, a counterinsurgency blitz aimed at quelling a Taliban resurgence. It is the largest military offensive since the 2001 ouster of the former regime.

"We are the focus of Mountain Thrust right now," said Capt. Jared Wilson. "This is the decisive part of the operation because if we do not get on the mountain, we will not be able to accomplish this mission."

The open-ended offensive aims at hunting down Taliban fighters blamed for the deadliest spate of militant violence since 2001, marked by ambushes and bombings.

More than 500 people, mostly militants, have been killed in the past month as insurgents launched increasingly bold attacks against coalition forces, and fighting intensified. More than 90 suspected militants have been killed in the past few days, the military says. At least nine coalition soldiers have been killed since mid-May.

On Sunday, Taliban militants fatally shot a former chief of one of Helmand province's districts and four bodyguards in an ambush of their convoy, said provincial spokesman Ghulam Mohiudin.

The slain official, Jama Gul, had been traveling along the highway between Sangin and Grishk districts.

Southern Helmand was also the scene of fighting Saturday, when British troops killed six Taliban fighters near Kajaki dam, British spokesman Capt. Drew Gibson said Sunday.

In the past few days, militants had been firing mortars in an attempt to damage the dam, Gibson said, adding that British forces "have tightened security in this area."

In nearby Zabul province, a joint operation between police and coalition forces in Shahjoy district killed two suspected militants. Two other wounded insurgents were arrested, said provincial police chief Noor Mohammed Paktin.

Before boarding the U.S. helicopters, Wilson warned his troops about the danger of their new mission.

"I want you to understand the seriousness of what you are about to do. We are landing fully loaded CH-47s on the top of a mountain. This is a highly dangerous mission. On the top of those dangers, we're going to an area where no one has been for years," he said.

Their new encampment is remote — more than 60 miles from the nearest ground forces — but Wilson said that serves as an advantage.

"The enemy did not suspect we would come up here. They believe they have a safe haven area up here because it has been untouched by coalition troops for years," he said.

On the mountain ridge, soldiers were busy setting up defense positions and firing mortar rounds into the valleys to test their artillery.

Manning an M-16 rifle on a ridge line as he looked down into the valley below at a smattering of mud huts, Spc. Daniel Borisow, 23, from Akron, New York, said he was ready to fight.

"For once we are in the position where we're going to take the fight to the enemy instead of us rolling through [in Humvees] and them attacking us," he said.