US president Barack Obama has asked the Pentagon to make plans to withdraw all troops from Afghanistan by the end of the year in case the US and Afghanistan cannot complete a bilateral security agreement.
Obama discussed the plans with Afghan president Hamid Karzai, who has so far refused to sign the security agreement.
The White House says Obama told Karzai that he was open to the possibility of finalising the agreement later this year, most likely after the Afghan elections this spring.
If an agreement is signed later this year, Obama told Karzai the US could keep a limited troop presence.
But he says the longer it takes to reach a security accord, the more likely it will be that any military presence beyond 2014 is "smaller in scale and ambition".