American defence secretary Leon Panetta says he hopes US troops in Afghanistan can end their combat role by 2013 - 18 months before the NATO mission is due to end.
Speaking while travelling to a NATO summit, Leon Panetta said the US hoped to switch to a role training and supporting Afghan forces.
His comments are the first time a senior US official has given a timetable for transition.
Some 68,000 troops are due to remain in Afghanistan after the end of 2012.
There are currently some 99,000 US troops in the country, with 22,000 scheduled to return home during this year.
Mr Panetta said the US would maintain an "enduring presence" in Afghanistan after its combat troops had come home, and said the 2014 deadline was a pan-NATO ambition that all member states were aiming to meet.
A BBC correspondent says it's a clear indication of the US government's desire to reduce its military presence in Afghanistan as early as possible.