The aircraft was supporting the Nato mission in the country when it went down in the southern province of Kandahar.

"The Ministry of Defence is extremely sorry to have to confirm that the aircraft lost in Afghanistan earlier today ... was British, and that the crash led to 14 fatalities," a ministry spokesman said in London.

He said the dead Britons were 12 Royal Air Force (RAF) personnel, a Royal Marine and an army soldier.

British Defence Secretary Des Browne called the accident 'dreadful and shocking'.

"This is not the time for specula tions, as the operation to secure the crash site is ongoing," he said in a statement.

"I can say, however, at this stage all the indications are that this was a terrible accident and not the result of hostile action," he added.

The crash was Britain's worst single loss in Afghanistan and caps a month in which British forces in the country have suffered severe casualties.

Nato said in a statement the British plane was supporting the alliance-led International Security Assistance Force and crashed after declaring a technical problem.

"Enemy action has been discounted at this stage," it said.

The crash came at a time when the Taliban and other insurgent and criminal groups have stepped up attacks on Afghan and foreign forces, plunging the country into its bloodiest period since the Taliban were toppled in late 2001.

About 2,000 people, most of them militants but also including civilians, Afghan forces, aid workers and more than 90 foreign soldiers, have been killed in violence this year.

Suspected Taliban fighters yesterday assassinated a senior Afghan police officer, his three bodyguards and a female relative, leaving only the woman's three-month-old baby alive.

"They were definitely Taliban. No one can carry out such a cowardly ambush except the Taliban," said Sayed Agha Saqib, the police chief of the south-western province of Farah.

Suspected Taliban also assassinated a district police chief in neighbouring Nimroz province, killing three of his bodyguards. Three attackers were also killed, police said.

Britain has faced unexpectedly fierce resistance from Taliban fighters since sending the first large foreign force to Helmand this year as part of an expanding Nato peacekeeping mission in the alliance's biggest ever ground operation.