Afghanistan's President Hamid Karzai has refused to sign a security deal with the US, the White House said, and Washington may have to resort to the "zero option" of withdrawing all American troops from the strife-torn country next year, as it did in Iraq.

Karzai told US National Security Advisor Susan Rice in Kabul on Monday that the US must put an immediate end to military raids on Afghan homes and demonstrate its commitment to peace talks before he would sign a bilateral security pact, Karzai's spokesman said.

The White House said Karzai had outlined new conditions in the meeting with Rice and "indicated he is not prepared to sign the (bilateral security agreement) promptly."

"Without a prompt signature, the US would have no choice but to initiate planning for a post-2014 future in which there would be no US or Nato troop presence in Afghanistan," a White House statement quoted Rice as saying.

On Sunday, an assembly of Afghan elders endorsed the security pact, but Karzai suggested he might not sign it until after national elections next spring.

The impasse strengthens questions about whether any US and Nato troops will remain after the end of next year in Afghanistan, which faces a still-potent insurgency waged by Taliban militants and is still training its own military.

US troops have been in Afghanistan since leading multinational forces in ousting the Taliban regime in late 2001.

Just over two years ago, US President Barack Obama pulled the plug on talks with Iraq about keeping a residual American force there after that war. In October 2011, when he announced that decision, there were more than 40,000 troops in the country. By the end of the year, they had all been withdrawn.

In Afghanistan, there are still 47,000 American forces. The United States has been in discussions with Afghan officials about keeping a small residual force of about 8,000 troops there after it winds down operations next year.

US officials, including Secretary of State John Kerry and Defense Secretary Chuck Hagel, have said the bilateral security deal with Afghanistan must be signed by year-end to begin preparations for a post-2014 presence.

Rice, who made a three-day visit to Afghanistan to visit US troops, told Karzai it was "not viable" to defer signing the deal until after the election, the White House said.

The delay "would not provide the United States and Nato allies the clarity necessary to plan for a potential post-2014 military presence," the White House said. - Reuters