A hidden enemy frustrates efforts to rebuild Afghanistan

"Effing brilliant," said a Royal Marine as J Company, 42 Commando, returned to base from their heaviest clash with the Taliban since they arrived in Afghanistan a month ago. Their elation and relief was understandable, but the engagement also showed the movement remained a threat, even in the relatively secure centre of Helmand province.

Up to a dozen Taliban fighters were believed killed. No marines were hurt, but the company found an Afghan civilian with a leg wound lying in the road after the encounter. He was brought to the Gereshk base and evacuated by helicopter to the hospital at Camp Bastion, the main British base in Helmand.

The encounter began yesterday afternoon as the company was completing a patrol on the eastern bank of the Helmand river about six miles outside Gereshk, an area known to be heavily infiltrated by the Taliban. "Just as we were returning to our vehicles, we came under mortar fire from two positions, one on each side of the river," said the company commander, Major Ewen Murchison.

"At first the fire was inaccurate, but then it started coming closer to us, and one shell fell 25 metres from some of the men. We saw a group of five to seven armed individuals down on the river bed, who were signaling with mirrors to the mortar crews, apparently to direct their fire. We neutralised them with machine-gun fire. One of the mortars was in range, and we neutralised that too." Although two RAF Harriers were scrambled from Kandahar air base, the pilots could not identify the second mortar, which was mounted on a truck. Major Murchison said he decided against a follow-up operation, which could have run into a prepared ambush, and casualties could not be verified.

"Every time we've gone out in force before, they've always moved out," said one of J Company's officers, Captain Tom Vincent. "This was the first time they've been prepared to stand up and have a go. That's why the lads are so happy." His commander added that for some of the younger men, "it was the first time they've heard the thump of a mortar and the whizz of the shell going past. It's an interesting sound if you've never heard it before."

Rarely, though, are encounters between British forces and armed Afghans so straightforward. Major Murchison described an incident earlier in the patrol, when they detained an Afghan with a shotgun who appeared to be passing on their movements by mobile phone. Although they found two AK-47 ammunition clips beneath his bed when they searched his home, they could not find any clear evidence that the man was connected to the Taliban or the opium trade, and he was released. It lent force to the major's comment that "it is difficult to distinguish between the Taliban and ordinary hoods".

Gereshk, the commercial capital of Helmand, is an important target for the Taliban, because it straddles a strategic intersection. "But they do not need to take the town," said the marines' commander. "They can sit outside and have an influence, both economically and through intimidation. It is our job to restrict their freedom of action and allow the Afghan security forces to build up competence and confidence."

The death of a marine in a suicide bombing in the provincial capital, Lashkar Gah, this month signalled that British forces faced a new threat, although Major Murchison said he was more concerned about roadside bombs, three of which had exploded in Gereshk in the past three weeks.

As for the main mission of British troops in Helmand, to support development, the major made it clear that only a handful of smaller projects were possible at the moment.