美国从阿富汗撤出所有部队

US President Barack Obama is putting more pressure on Afghan President Hamid Karzai when it comes to the United States' involvement in Afghanistan following this year.

The White House says Obama has placed a call to Karzai, telling the Afghan president the US is now beginning its preparations for a full withdrawal of troops by the end of the year.

This comes as Karzai continues to avoid signing a Bilateral Security Agreement which would see some US troops say behind following the scheduled withdrawal of NATO forces by the end of this year.

Obama has reportedly told Karzai that the longer he waits, the fewer US troops will remain behind.

White House spokesperson Jay Carney.

"The fact that President Karzai has indicated that it is unlikely he will sign the BSA (Bilateral Security Agreement) means that if he doesn't sign, it is at least possible that a successor Afghan government might sign it. But that pushes us later into the year and the longer we go, without a signed BSA, by necessity the more narrow in the size and ambition the mission for a post 2014 force would be."

The unsigned Bilateral Security Agreement would keep about 10-thousand U.S. troops in Afghanistan in a support role for 10 years.

Karzai has been refusing to sign the deal, saying he needs concessions from US forces about raids in the country.