The US government has insisted that President Barack Obama has made no final decision on his new strategy for Afghanistan.
This follows speculation that Mr Obama is set to approve a request from US military commanders to send an extra 40,000 troops.
Yesterday, Britain said it would send an additional 500 troops to the country.
But officials in Washington say some advisors are emphasising that the main threat to US interests in Afghanistan is al-Qaeda, not the Taliban.
A recent reduction in the number of forces in Iraq has eased the strain on the US military somewhat.
However, a serious build-up in Afghanistan would pile pressure on the country's armed forces.
US army chief of staff General George Casey acknowledged earlier this month that a large injection of troops into Afghanistan could make it more difficult to preserve time between tours.
Pentagon press secretary Geoff Morrell said President Obama, Defence Secretary Robert Gates and military leaders were 'very mindful of the continued stress and strain on our forces throughout these eight years and two wars'.
Senior officers have blamed repeated deployments and relatively brief periods spent at home between combat tours for contributing to an increase in suicides among US soldiers.
