Helicopter fly over Afghanistan
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How will US troops be able to leave Afghanistan?

The US Vice President Joe Biden has said the US troop presence in Afghanistan will be '''totally out of there, come hell or high water, by 2014".

His comments came just two weeks before the end of the 'critical year in Afghanistan'.

Withdrawing the troops is a political aspiration for the Obama administration but how will this be possible?

Nik Gowing reports.