Chairman of the US Joint Chiefs of Staff Admiral Mike Mullen has said 20,000 to 30,000 extra troops may be sent to Afghanistan by the beginning of next summer.
Washington is already sending 3,000 extra troops in January and another 2,800 by spring, but officials previously have said the number would be made up to 20,000 in the next 12 to 18 months, once approved by the US administration.
US Army General David McKiernan has asked for the extra troops to halt a growing Taliban insurgency particularly in the east and south of Afghanistan.
President-elect Barack Obama has pledged a renewed focus on Afghanistan, where US-led forces toppled the Taliban government in late 2001 after the 11 September attacks.
The US has about 31,000 troops in Afghanistan, some operating independently and some as part of a 51,000-strong NATO-led force.
After the January deployment, most of the reinforcements are to be sent to southern Afghanistan to bolster mainly British, Canadian and Dutch troops who have suffered heavy casualties in the last two years fighting in the Taliban heartland.
