A senior White House official has said the US would consider leaving no American troops in Afghanistan after the end of combat in December 2014.

The official, however, stressed that the administration remains committed to preventing the country from becoming a haven for al-Qaeda.

The comments on Tuesday came as Afghan President Hamid Karzai headed to Washington for talks with his US counterpart Barack Obama.

Asked whether Obama would consider a scenario in which all US troops left and there was no residual force in Afghanistan, Ben Rhodes, a deputy national security adviser said: "That would be an option we would consider."

"We wouldn't rule out any option. We are not guided by the goal of a certain number of troops in the country. We are guided by the objective that the president has set," Rhodes told reporters.

Obama's goals are to ensure that Afghanistan's new national army has the capacity and equipment to defend itself and to ensure that al-Qaeda cannot make a post-war comeback.

Al Jazeera's Patty Culhane, reporting from Washington, said that that senior administration officials told reporters in a conference call that if the two main missions of strengthening Afghan security forces, and conduct counterterrorism operations were complete, there would not be a need for troops.

US and international forces anticipate ending combat missions in Afghanistan this year, before moving to a training role with local forces until the end of 2014.

Officials have said the White House appears to favour keeping fewer than 10,000 US troops in Afghanistan, but until now the administration has not said publicly it is considering a so-called zero option.

Pressure growing

Pressure is growing on Obama to end the war rapidly due to deep war weariness in the US, tightening military budgets and anger over "insider attacks" by Afghan troops on the NATO-led soldiers.

"If Mr Obama cannot find a way to go to zero troops, he should approve only the minimum number needed," The New York Times said in an editorial this week that called Karzai's government "profoundly corrupt".

Obama will host talks with Karzai at the White House on Friday, the day after the Afghan president meets Secretary of State Hillary Clinton.

US officials have said a decision could be made during Karzai's visit on how many troops stay on in Afghanistan after 2014.

The talks will also include equipping and strengthening Afghan forces, efforts to negotiate peace with Taliban-led insurgents and a long-term security agreement with the US, Karzai's office said.

The number of foreign soldiers fighting in Afghanistan has already fallen to 100,000 from about 150,000. Of those, 66,000 are US troops, down from a maximum of about 100,000.

Karzai has expressed support for keeping some US troops in Afghanistan after 2014 but sensitive details - including immunity for American soldiers and the transfer of detainees into Afghan custody - are still under negotiation.

Washington scrapped plans for some troops to remain in Iraq after Baghdad refused to grant US soldiers immunity from prosecution.