London: British troops transferred responsibility for security in the Sangin district of southern Afghanistan to US forces Monday, leaving an area where Britain suffered its worst losses since the invasion.

The military insisted that the handover was not an admission of defeat after four years of fighting with Taliban insurgents following the British arrival in the dusty market town in Helmand province in 2006.

“British forces have served in Sangin over the last four years and should be very proud of the achievements they have made in one of the most challenging areas of Afghanistan,” British defence minister Liam Fox said.

“The level of sacrifice has been high and we should never forget the many brave troops who have lost their lives in the pursuit of success in an international mission rooted firmly in our own national security in the UK.”

More than 100 British troops have died in Sangin district, accounting for nearly a third of their total 337 casualties since the invasion of Afghanistan in 2001 to topple the Taliban regime following the September 11 attacks.

After the handover to the US Marine Corps on Monday, the estimated 1,000 British Royal Marines in Sangin will be redeployed to central Helmand, another hotspot for insurgent violence and opium production, the military said.

Asked if the move was an admission of defeat, defnce ministry spokesman Major General Gordon Messenger told BBC radio: “It certainly won’t look like that on the ground.”

Colonel Stuart Tootal, a retired British army officer who commanded the first battle group of 1,200 soldiers sent into Sangin four years ago, also rejected talk of submission.

“This is a handover, not a pullout,” he told the BBC.

“Despite the emotional attachment to Sangin, and the job’s not finished yet and the Americans will continue it on, it’s not a defeat in any way at all.

“That’s from someone who served there and I lost half of my soldiers who were killed here (in Afghanistan) in Sangin.”

British forces faced some of their fiercest fighting since World War II in Sangin as they tried to flush out insurgents and curb opium production.

They were also trying to secure electricity lines from an under-construction dam that would have supplied energy for much of southern Afghanistan.

The Ministry of Defence said that since 2006 there had been reform of local governance and improvement in services, while twice as many shops were now open in the town’s bazaar compared with last year due to increased security.

“Our troops operating in Sangin have been taking the fight to the Taliban and by doing so have reduced the threat of violence spreading elsewhere,” Messenger said in a statement.

But in a warning to the US forces taking over the area, he said that the area “is and will continue to be a challenging area because of its strategic importance to the Afghan Government, ISAF and the insurgency”.

In July the Taliban claimed that British troops were pulling out of Sangin because of pressure from the militants’ attacks, adding that it was the “start of the British forces’ defeat in Afghanistan”.

Britain has 8,000 troops in Helmand, the lion’s share of its 9,500-strong force in Afghanistan, which comes under the command of ISAF.