Nato has handed over security for the whole of Afghanistan for the first time since the Taliban were ousted in 2001.
At a ceremony in Kabul, President Hamid Karzai said that from Wednesday "our own security and military forces will lead all the security activities".
Observers say the best soldiers in the Afghan army are up to the task but there are lingering doubts about some.
International troops will remain in Afghanistan until the end of 2014, providing military back-up when needed.
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