Senior US government figures have rejected criticism of President Barack Obama's plan to start withdrawing troops from Afghanistan in 2011.

美国政府高级官员驳回了奥巴马总统2011年从阿富汗撤军的评论。

Robert Gates and Hillary Clinton were defending President Obama's plans

President Obama announced last week that the US would boost troop numbers, but start pulling out撤离 by July 2011.

State Secretary Hillary Clinton said it was not a "drop-dead吸引人的 deadline", while Defence Secretary Robert Gates said it was "the beginning of a process".

Mr Gates also said the whereabouts下落 of Osama Bin¹ Laden² were unknown.

He said it had been "years" since the US last had any good intelligence about his movements.

'Wrong message'

Republicans have criticised President Obama's date as being "arbitrary任意的，恣意的" and a possible encouragement for the Taliban.

Senator John McCain said it sent the wrong message to the militants³.

There has also been concern in Afghanistan that its government would not be ready to cope in the event of倘若，万一 a speedy US exit.

Correspondents say the Afghan government and security forces recognise that the country is at a critical juncture⁴节骨眼 - the Taliban have continued to gain strength, and although there is little enthusiasm for extra troops, officials recognise they are unable to deal with the situation on their own.

Mr Gates emphasised that "there was no deadline", and that the handover of responsibilities to Afghan authorities district by district would be based on "conditions on the ground".

He said troops would be sent home gradually, with the US retaining an "overwatch" position if necessary.

"[President Obama] was balancing a demonstration⁵ of resolve with also communicating a sense of urgency to the Afghan government that they must step up to the plate in terms of recruiting their soldiers, training their soldiers and getting their soldiers into the field."

Bid for 'patience'

He added that in July 2011 US generals will know "whether our strategy is working".

Afghan President Hamid Karzai, whose government has been plagued折磨，麻烦 by allegations of corruption⁶, said: "Afghanistan welcomes this new strategy, and Afghanistan will do all it can to be a good partner in it."

But he warned the international community to have "patience with us and the realisation of the realities in Afghanistan.

"If it takes longer, then they must be with us," he said on CNN.

Mr Obama ordered 30,000 more US troops to Afghanistan as quickly as possible, bringing US troop strength in the country to more than 100,000.

Announcing the surge, he said the mission in Afghanistan was to defeat al-Qaeda, reverse颠倒，逆转 the Taliban's momentum⁷动力，要素 and deny them the ability to overthrow推翻 the government.

Secretary of State Hillary Clinton, also in the studios on Sunday, said: "We're not talking about an exit strategy or a drop-dead deadline.

"What we're talking about is an assessment⁹ that... we can begin a transition过渡，转变, a transition to hand off responsibility to the Afghan forces."