Obama in Kabul: US-Afghan pact shows 'enduring commitment'
US President Barack Obama has arrived in Afghanistan on a previously unannounced visit.
He is to sign an agreement with Afghan President Hamid Karzai that will outline the US role in the country after 2014, when most Nato combat forces are due to pull out.
The BBC's Quentin Sommerville says it is a key move showing that America's enduring commitment to Afghanistan remains.