NATO's secretary general has echoed a US announcement that it is planning to withdraw all of its troops from Afghanistan if a security deal cannot be agreed with the Afghan government.

The blunt statement from Anders Fogh Rasmussen on Wednesday ratchets up pressure on the Afghan president, Hamid Karzai, to strike a deal with the US.

On Tuesday, The US president, Barack Obama, threatened to withdraw all US troops from Afghanistan by the end of this year if a pact wasn't signed.

Without that agreement, Rasmussen said, forces from other NATO countries and partners could not stay beyond 2014 either, There are roughly 19,000 non-US troops now in Afghanistan.

"Let me stress, this is not our preferred option ... but these are the facts," said Rasmussen.

Obama told Karzai by telephone the Pentagon had little option but to draw up a contingency plan for a full withdrawal because the Afghan leader had refused to sign a Bilateral Security Agreement with Washington.

"Specifically, President Obama has asked the Pentagon to ensure that it had adequate plans in place to accomplish an orderly withdrawal by the end of the year," the White House was quoted as saying by Reuters.

The US has been pushing for legal immunity for its soldiers and contractors, a point resisted by Karzai.

Source: Agencies