America’s ambassador to Afghanistan yesterday expressed deep unease over the British military’s cease-fire with the Taliban and subsequent withdrawal from a flashpoint town.

British troops moved out of the town of Musa Qala in north Helmand last week after a truce negotiated by tribal elders acting as intermediaries with the militia. After months of heavy fighting in which eight British soldiers and hundreds of Taliban fighters died, they handed over to an Afghan militia raised from local men.

Both the original decision to send troops to outposts — “platoon houses” — and the deal proved highly contentious. It is understood that another such arrangement is being negotiated in another hotspot, Sangeen.

In an interview with the Daily Telegraph, Ronald Neumann said: “There is a lot of nervousness about who the truce was made with, who the arrangement was made with, and whether it will hold.”

He said the “jury is out” over whether the deal can be seen as a positive move.

Mr. Neumann said repercussions of the takeover by local forces must be “rigorously tested” to ensure that Musa Qala had not simply morphed into “a sanctuary for an area governed by the Taliban.”

British commanders have denied that the Taliban were directly involved in the truce negotiations, which they say were conducted alongside the governor of Helmand with local tribal elders. NATO officials have briefed journalists that local tribal elders in Musa Qala forced the Taliban to stop fighting.

The summer saw intense fighting across Helmand, where 4,300 troops are based as part of a NATO campaign to end the insurgency and begin reconstruction.

British forces have fired close to half a million rounds. More than 1,000 Taliban fighters are estimated to have died in the fighting, which has also seen 17 British soldiers killed and more than 70 injured.

Mr. Neumann said that an American and NATO analysis earlier in the summer indicated that in areas of the south such as Helmand, local tribes were siding with the Taliban because of grievances over local bad governance. “If you just say anyone who is sympathetic to the fight on the other side is forever outside the pale of negotiation you rather shoot self in foot,” he said.

“But at same time, if you have an area that is under the Afghan government flag but is not under the actual authority of the Afghan government, then you are losing in a very big way.

“[The truce] certainly shouldn’t be replicated until those questions have been answered.”

There is also a high degree of nervousness in the Afghan government about the Musa Qala deal, with ministers comparing it warily to truces with the Soviet army in the 1980s, which mujahedeen commanders used to build up their forces and gain a tactical advantage.

Brigadier Ed Butler, the outgoing commander of British forces in Helmand, said after the initial truce was agreed last month: “I fully acknowledge that we could be being duped; that the Taliban may be buying time to reconstitute and regenerate. But every day that there is no fighting, the power moves to the hands of the tribal elders who are turning to the government of Afghanistan for security and development.”