Afghan forces should start taking responsibility for security in areas of their country this year and be in charge of all provinces by the end of 2014, an international conference agreed today.
Ministers from more than 70 nations endorsed the strategy for the withdrawal of Nato-led foreign troops - including about 10,000 from the UK - at a major summit in Kabul.
British Foreign Secretary William Hague told the gathering that the handover should be able to "start soon". He later reasserted the Government's desire to have all UK combat troops out within five years.
Earlier, Afghan President Hamid Karzai said: "I remain determined that our Afghan national security forces will be responsible for all military and law enforcement operations throughout our country by 2014."
The Kabul conference agreed a communique backing Mr Karzai's target and stating that conditions would be examined with a view to launching the security transition by the end of 2010.
Mr Hague, addressing the conference this morning, said: "The transition to full Afghan security responsibility should be gradual and determined by Afghan capability, but it should be able to start soon.
"For our part, the UK will continue to provide support and training to the Afghan security forces until that goal is achieved."
Speaking later on the BBC Radio 4 Today programme, he added: "We are trying to make sure that the Afghan state can look after itself in the future so that our forces don't have to be here in the long term.
"I think it is possible for them to be able to run the country and that's why we are saying in five years' time we won't have our combat troops in action here in Afghanistan."
Prime Minister David Cameron has already indicated that he wants the bulk of Britain's detachment in Afghanistan to come home by 2015.
Today's conference comes in one of the bloodiest periods for international forces since the toppling of the Taliban administration in 2001, with 13 British deaths this month alone.
But the fact that Afghanistan was able to host its first high-level gathering in the capital was viewed in Whitehall as a mark of the security progress already made.
Nato secretary-general Anders Fogh Rasmussen said the handover would be based on "conditions, not calendars".
US Secretary of State Hillary Clinton said President Barack Obama wanted a "responsible conditions-based transition to Afghan security leadership in July 2011".
"The transition process is too important to push off indefinitely," she said.
"But this date is the start of a new phase, not the end of our involvement."