US Defense Secretary Ashton Carter's comments offered the clearest sign yet that Washington was ready to delay the closure of some bases and retain more troops on the ground after appeals by Afghanistan's new President Ashraf Ghani and advice from commanders.
To safeguard "hard-won" progress, Obama "is considering a number of options to reinforce our support for President Ghani's security strategy, including possible changes to the timeline for our drawdown of US troops," Carter said.
Apart from troop numbers, the United States and its allies would need to make "long-term commitments in resources, equipment and other support" to ensure the success of the Afghan forces, he said.
Only days after taking the helm as defence secretary, Carter paid an unannounced visit to a country where US troops have fought for more than 13 years but are now in a scaled back role.
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But the Obama administration already has delayed the pace of the withdrawal, allowing 1,000 additional American forces to remain this year.
And the US commander on the ground, General John Campbell, has suggested he favours slowing the drawdown further, though the details of the possible options before Obama remain unclear.
Carter said as part of the review of the pullout plan, Washington was also was "rethinking the details of the counter-terrorism mission" that currently targets Al-Qaeda militants with raids by US and Afghan special forces and drone strikes.
He said the single most important factor that had prompted the review of the troop withdrawal timetable was the formation of a unity government last year led by Ghani, which he said had introduced "certainty" and "predictability".