President Barack Obama has promised to speed up a transfer of lead security responsibility from NATO to Afghan forces this spring, in a sign the pace of US troop withdrawals could quicken.
After meeting Afghan President Hamid Karzai on Friday, Obama said NATO forces would have a "very limited" role in the country after 2014 and insisted that Washington had achieved its prime goal of "decapitating" al-Qaeda.
The leaders met at a crucial moment in the final chapter of a long, bloody war, and as Obama balances the future security of Afghanistan with US combat fatigue and a desire to spend America's dwindling resources at home.
"Starting this spring, our troops will have a different mission - training, advising, assisting Afghan forces," Obama said.
"It will be a historic moment and another step toward full Afghan sovereignty."
Obama said any agreement on troop withdrawals must include an immunity agreement in which US troops are not subjected to Afghan law.
The president said the path of the US military remains clear and the war is moving toward a "responsible end" in 2014.
US commanders in Afghanistan have proposed keeping 6,000 to 15,000 US troops after 2014 to continue pursuing armed groups and training Afghan security forces.
The White House tends to favour lower troop levels than military generals.
US officials have said privately that the White House is asking for options to be developed for keeping between 3,000 and
9,000 troops in the country.
General John Allen, the top US and NATO commander in Afghanistan, had initially suggested that as many as 15,000 troops should remain - a number Obama would likely have a hard time selling to a war-weary US public.
With some 66,000 US troops currently in Afghanistan, Obama is also deciding on the pace of this year's troop reductions.
NATO allies are also steadily reducing troop numbers and Afghan forces are due to take the lead role in security across the country in 2013.
However, doubts remain about their ability to shoulder full responsibility.
Officials say Obama would be open to pulling all US forces out of Afghanistan at the end of 2014.