The military insisted that the handover of the flashpoint area of Helmand province, first announced in July, was not an admission of defeat after four years of fierce fighting since British forces moved there in 2006.[break]
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 nearly nine years ago.
"ISAF (the NATO-led International Security Assistance Force) has today announced that British forces in southern Afghanistan have handed responsibility for security in Sangin to US forces," a ministry statement said.
Defence Minister Liam Fox said the handover "represents sound military rationale", adding that British troops will be redeployed away from the market town and surrounding areas into central Helmand.
Around 1,000 Royal Marines will leave the area after handing over control of security for Sangin to the US Marine Corps.
"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," said Fox.
"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."
British forces faced some of their fiercest fighting since World War II in and around Sangin as they tried to flush out Taliban insurgents and clamp down on opium dealers.
They were also trying to secure electricity lines from an under-construction dam that would have supplied energy for much of southern Afghanistan.
The defence ministry 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," said Major General Gordon Messenger, spokesman for the British chiefs of staff.
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.
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