Obama in Afghanistan: 'We must replace war with peace'

US President Barack Obama has signed a strategic agreement with Afghan leader Hamid Karzai on a previously unannounced visit to Afghanistan.

The 10-year accord outlines military and civil ties between the countries after the end of Nato's mission in Afghanistan in 2014.

Speaking in Kabul, President Obama acknowledged that there would be "difficult days ahead" but that Afghanistan had a "friend and partner in the United States".

He said that the US could achieve its goal of denying al-Qaeda a safe haven, but also "wind down this war and usher in a new era of peace in Afghanistan".