British and Nato defence officials have consistently expressed concern about US tactics, notably air strikes, which kill civilians, sabotaging the battle for "hearts and minds" and infuriating Hamid Karzai, the Afghan president.

Des Browne, the defence secretary, recently raised the issue with Robert Gates, his US counterpart, and Jaap de Hoop Scheffer, Nato's secretary general, admitted last month that an increasing number of civilian casualties was undermining support for alliance troops.

He said Nato commanders had changed the rules of engagement, ordering their troops to hold their fire in situations where civilians appeared to be at risk.

Today, a senior British commander was quoted in the New York Times as saying that in Sangin, in the north of Helmand province, which had been calm for a month, there was no longer a need for special forces. "There aren't large bodies of Taliban to fight any more," he said.

"We are dealing with small groups and we are trying to kick-start reconstruction and development."

Twelve-man teams of US special forces had been criticised for relying on air strikes for cover when they believed they were confronted by large groups of Taliban fighters and their supporters.

Unnamed British officers were quoted today as saying the US had caused the lion's share of casualties in their area and that after 18 months of heavy fighting since British forces arrived in Helmand they were finally making headway in securing key areas, but were now trying to win back support from people whose lives had been devastated by bombing.

The newspaper estimated the number of civilian casualties this year in Helmand at close to 300 - most caused by foreign and Afghan forces, not the Taliban. Human rights and aid groups estimate that 230 Afghan civilians were killed throughout the south of the country last year.

Nato officers admit they are troubled by the high toll. One medic told the Guardian that during a 14-day period last month, British soldiers rescued 30 Afghan civilians wounded in bombings or firefights - half of whom were children.

The US and Nato today denied the British commander had asked US special forces to leave his area of operations. However, Mr Browne, visiting British and Nato troops in Afghanistan, said the commander was expressing a personal view.

"It is the reporting of an observation of a British officer on a particular part of the American military," he told reporters in Kabul.

"That may be his view, but it is not the view of the Helmand taskforce commander, it is not the view of our government, it is not the view of the Americans, it is not the view of the alliance. These things can be said in the heat of battle. These are very difficult circumstances."

After a meeting with Mr Karzai, Mr Browne said the British-led Helmand force has made "enormous progress in driving back the Taliban in the north of the province".

He added: "The forces' progress has been followed by targeted development projects that are making a difference to ordinary Afghans' lives."

British officers say US special forces are cavalier in their approach to the civilian population. The tensions were illustrated by an incident the Guardian witnessed in Sangin earlier this summer.

A British patrol was abandoned by its American special forces escort in the town for several hours. Stranded in central Sangin, British officers tried to establish radio contact with the Americans, who had disappeared without warning, and swore impatiently when they could not.

The British criticisms intensified after the Americans led them to their proposed site for a new Afghan patrol base in the town - beside a graveyard and a religious shrine. "Sensitivity is not their strong suit," said one British officer.

Most British soldiers work well with regular American troops and some speak admiringly of them. But US special forces units are a different matter.

They operate under a different chain of command, with their own rules on everything from dress code to the use of weapons. Whereas the British troops operate under Nato command, American special forces are commanded by the US-led coalition in Bagram airbase outside Kabul. That means the Americans can call on a wider range of airstrikes, and also that British officers have little control over which munitions are dropped in populated areas.

The British military spokesman in Helmand, Lt Col Charlie Mayo, said the special forces had supported seven British-led operations in Helmand since last April. He said that relations between the two sides were "excellent".

"To work together effectively we have to have bloody good cooperation and we have to mutually support each other," he said. Col Mayo stressed that the British commander who had a problem with special forces had requested them to leave Sangin town only, not all of Helmand.

Officers also argue that where Taliban fighters mount ambushes from inside heavily populated areas, civilian deaths are unavoidable. "When you are working in a high intensity counter-insurgency environment like this, regrettably you are going to have civilian casualties," Col Mayo said.

In London, British officials confirmed UN forecasts that southern Afghanistan's opium poppy crop, based in Helmand, will exceed last year's record. Foreign Office minister Lord Malloch Brown described the figures as "extremely disappointing".