Discussions were initiated before the killing of Osama bin Laden on May 2 but American and British diplomats believe that the death of the al-Qaeda leader could give added impetus to the talks and the drawdown of Nato troops, due to begin in July.

Taliban fighters pose with weapons at an undisclosed location in southern Afghanistan, May 5, 2011. A Western official in Kabul confirmed the United States was in direct contact with the Taliban following a sea change in American policy this year. (REUTERS/Stringer) President Barack Obama, whose hand has been strengthened by the successful operation to bring bin Laden to justice, is believed to be contemplating a withdrawal of several thousand American troops, some 100,000 of whom are in Afghanistan.

David Cameron has made clear he is prepared to follow suit with a withdrawal of a proportionately similar number of British troops. There are currently about 10,000 British personnel in Afghanistan, most of them concentrated in central and southern Helmand.

Previous talks broke down when a supposed Taliban leader flown into Kabul in a Nato plane was revealed to be a shopkeeper trying to make some money. Other attempts at dialogue have foundered because would-be emissaries could not be confirmed as genuine.

But American officials told the "Washington Post" that although these new talks were preliminary they were with Taliban officials with a direct line to Mullah Omar, the one-eyed leader of the Taliban's Quetta Shura rilling council.

A Western official in Kabul confirmed the United States was in direct contact with the Taliban following a sea change in American policy this year.

Marc Grossman, the replacement for special envoy Richard Holbrooke, has been nicknamed "Mr Reconciliation" and told to focus efforts on trying to facilitate a political deal which would ease a US exit.

"Those are no longer preconditions, they are being seen as negotiated outcomes," said the Western official. At the same time, the Taliban has weakened its demand that no talks can take place before foreign troops leave.

Speculation about talks has angered opponents of President Hamid Karzai of Afghanistan, who say that they undermine Afghan democracy. Any peace deal with the Taliban is likely to involve some element of the group sharing power in Kabul. The Taliban has demanded the release of 20 prisoners from Guantánamo Bay.

American officials said that members of the brutal Haqqani network, based in North Waziristan across the border with Pakistan, have not taken part in the discussions.

In February, Hillary Clinton, the US Secretary of State, said the US would no longer insist on preconditions such as the need for the Taliban to renounce al-Qaeda and accept the Afghan constitution. Such declarations could be made after a deal had been reached.

The pursuit of "reconciliation" in Afghanistan will be high on the agenda in talks between Mr Obama and Mr Cameron in London next week.

Sir Nigel Sheinwald, the British ambassador to the US, said: "We are very keen to see the political track, the reconciliation track, given extra vigour in the months ahead along the lines of a speech given by Hillary Clinton in February when she talked about a diplomatic surge to follow the military surge."

The Foreign Office has long argued the case that a full handover of security to the Afghans by the target date of the end of 2014 will not be achieved without a settlement with the Taliban. By then, all 140,000 Nato troops currently in Afghanistan are due to have left.

British diplomats believe that the Americans have recently moved closer to London's position and have been encouraged by the efforts of Mr Marc Grossman.

"We believe the US will announce reductions in the months ahead and if that's possible the UK will be able to reduce some of its forces as well," said Sir Nigel.