General David Petraeus has handed over command of American and coalition forces in Afghanistan to General John Allen, transferring responsibility for the nearly 10-year war as Kabul's international allies draw up exit plans from the conflict.
Gen Petraeus stepped down after a one-year stint in charge of the more than 140,000 international troops in the country.
He was the architect of the counter-insurgency strategy which aimed to bring peace through an emphasis on decisive strikes against known insurgents and protecting the local population.
But as he left, it was unclear if either strategy had made Afghanistan safer. Violent attacks have continued, although international military officials argue they are not as widespread or as intense as they would have been otherwise.
Gen Allen, who officially took command at a ceremony in the capital, Kabul, said the drawdown of US forces which started earlier this month and the transition of some areas to Afghan control this week does not mean that international forces are easing up in their campaign to defeat the Taliban insurgency.
He said: "It is my intention to maintain the momentum of the campaign. There will be tough days ahead. I have no illusions about the challenges ahead."
The handover ceremony came as a bomb killed three international service members in the east, Nato said in a statement. It did not provide nationalities or further details. Most of the troops in the east are American. At least 37 international forces troops have been killed so far this month in Afghanistan.
It also took place just hours after security forces in Kabul killed the final attacker in the assassination of a close adviser to president Hamid Karzai. The Taliban claimed responsibility for the attack in which two gunmen shot adviser Jan Mohammed Khan and a politician he was meeting with in his house.
The deaths were announced on Sunday night and one attacker was quickly killed, but fighting continued inside the house until early on Monday as police tried to take out the remaining assailant who had barricaded himself in the house, police said. One police officer was killed, the Interior Ministry said.
The shooting and small explosions finally ended about 3am and reporters on the scene saw a body dragged out of the house on a plastic sheet. Afghan officials had originally said the attackers were wearing suicide vests but said on Monday that this was incorrect and they were armed only with guns and hand grenades.