US Marines battle on in Afghanistan

US Marines deployed into Taliban strongholds in a major assault in Afghanistan are in a "hell of a fight", said the commander of the operation.

The Brigade's 2/8 Infantry Battalion were facing difficult challenges, Brigadier General Larry Nicholson said on Friday.

"For 2/8 there is a hell of a fight going on in the southern quarter of the sector," he said.

The 1/5 Infantry Battalion met only light resistance in their push south and had already been able to meet locals at shuras (councils), Nicholson said.

"2/8 are going to face some challenges," he said on arrival at Garmsir, a town along the Helmand River that is a key objective for the air and ground assault.

Earlier on Friday, an officer said Taliban militants shot and damaged two unarmed marked medical helicopters charged with evacuating US Marines from the battlefield.

The choppers, marked with a red cross, were deployed on Thursday to fetch US soldiers suffering from heat stroke in the southern province of Helmand and came under Taliban gunfire as they approached, Colonel Mike Killion said.

Troops managed to destroy a militant position in the town on Thursday, said the commander of the Marine forces in Afghanistan.

"An enemy-controlled baseline just south of Garmsir was crushed yesterday but that doesn't mean all the enemy have gone," he said.

The offensive along 88km of Taliban-controlled areas in southern Afghanistan will test the Obama administration's new strategy of holding territory to let the Afghan government sink roots in Helmand.

The insurgency has proven particularly resilient in the area, and foreign troops have never before operated in such large numbers here. Large areas have been under Taliban control, with little or no government presence.

As the operation entered its second day, the units secured control of the district centres of Nawa and Garmser, and negotiated entry into Khan Neshin, the capital of Rig district, Pelletier said.

"They waited for the local and village elders," outside Khan Neshin and "with their permission they went in and now are engaged in talks", Captain Bill Pelletier said.

One Marine was killed and several others injured or wounded on the first full day of the assault on Thursday, the largest military operation in Afghanistan since the fall of Taliban government in 2001.