US General David Petraeus handed over command of NATO forces in Afghanistan on Monday.
The 58-year-old is leaving to become the new director of the CIA.
Petraeus took up the post last July after his predecessor, Stanley McChrystal, had to quit after he criticised several top US officials in an interview with Rolling Stone magazine.
Petraeus, who oversaw the troop surge in Afghanistan, will be replaced by US Marine Corps General John Allen.
The change in command comes as NATO troops begin a gradual handover of power to Afghan forces due to be completed by 2014.
That process started on Sunday with the central Bamiyan province, although it was overshadowed by the killing of a senior aide to President Hamid Karzai later that evening.
The Taliban on Monday claimed responsibility for murdering Jan Mohammad Khan in his own home in Kabul. He died during an attack on the building that lasted four hours.
Later on Monday President Karzai attended Khan’s funeral. The former governor of the southern Uruzgan province was buried within 24 hours of his death in line with Islamic tradition.
Khan’s murder came days after Karzai’s half-brother was shot dead by one of his bodyguards.