WASHINGTON: The Obama administration does not rule out a complete withdrawal of US troops from Afghanistan after 2014, the White House said on Tuesday, just days before President Barack Obama is due to meet Afghan President Hamid Karzai.

The comments by US Deputy National Security Adviser Ben Rhodes were the clearest signal yet that, despite initial recommendations by the top military commander in Afghanistan to keep as many as 15,000 troops in the country, Obama could opt to remove everyone, as happened in Iraq in 2011.

Asked about consideration of a so-called zero-option once the Nato combat mission ends at the end of 2014, Rhodes said: "That would be an option that we would consider."

Rhodes made clear that a decision on post-2014 troop levels is not expected for months and will be made based on two US security objectives in Afghanistan — denying a safe haven to al Qaeda and ensuring Afghan forces are trained and equipped so that they, and not foreign forces, can secure the nation.

"There are, of course, many different ways of accomplishing those objectives, some of which might involve US troops, some of which might not," Rhodes said, briefing reporters to preview Karzai's visit.

In Iraq, Obama decided to pull out all US forces after failing in negotiations with the Iraqi government to secure immunity for any US troops who would remain behind.

The Obama administration is also insisting on immunity for any US troops that remain in Afghanistan, and that unsettled question will figure in this week's talks between Obama and Karzai and their aides.

"As we know from our Iraq experience, if there are no authorities granted by the sovereign state, then there's no room for a follow-on US military mission," said Douglas Lute, special assistant to Obama for Afghanistan and Pakistan.

Jeffrey Dressler, an Afghanistan expert at the Washington-based Institute for the Study of War who favours keeping a larger presence in Afghanistan, questioned whether the White House comments might be part of a US bargaining strategy with Kabul.

"I can't tell that they're doing that as a negotiating position ... or if it is a no-kidding option," Dressler said. "If you ask me, I don't see how zero troops are in the national security interest of the United States."

Shouldn't Just "Leave Them"

US officials have said privately that the White House had asked for options to be developed for keeping between 3,000 and 9,000 troops in the country, a lower range than was put forward initially by General John Allen, the top US and Nato commander in Afghanistan.

Allen suggested keeping between 6,000 and 15,000 troops in Afghanistan.

Retired General Stanley McChrystal, a former US commander of the Afghan mission who resigned in 2010, said in an interview with Reuters on Monday there was a value to having an overt US military presence in Afghanistan after 2014 — even if it wasn't large.

"The art, I would say, would be having the smallest number so that you give the impression that you are always there to help, but you're never there either as an unwelcome presence or an occupier — or any of the negatives that people might draw," he said, without commenting on any specific numbers.

The United States now has about 66,000 troops in Afghanistan and Rhodes confirmed there would be steady reductions in troop levels through 2014.

Also on the agenda for the Obama-Karzai talks are tentative reconciliation efforts involving Taliban insurgents. Those efforts have shown flickers of life after nearly 10 months of limbo.

Still, hopes for Afghan peace talks have been raised before, only to be dashed. Last March, the Taliban suspended months of quiet discussions with Washington aimed at getting the insurgents and the Karzai government to the peace table.

Washington has also had a strained relationship with Karzai, who in October accused the United States of playing a double game in his country by fighting the war in Afghan villages instead of going after those in Pakistan who support insurgents.

Karzai will give a joint press conference with Obama on Friday and will visit the Pentagon on Thursday, meeting with Defence Secretary Leon Panetta and the US top military officer, General Martin Dempsey.

Still, it is unclear what, if any, concrete agreements might emerge from Karzai's visit to Washington.

Michael O'Hanlon, a defence analyst at Brookings, cautioned against expecting too much from the visit, which he said is best seen as an opportunity for Washington and Kabul to "shore up this partnership that has had such a troubled status and a weak foundation."

"There are a lot of scars in this relationship. There are a lot of hurt feelings," O'Hanlon said. "It's sort of like a bad marriage and it's very easy for just the wrong word to immediately set people off in an emotional way."