Chuck Hagel has arrived in Afghanistan in his first trip to the country as defense secretary.
Hagel landed in Kabul on Friday and he plans to meet with President Hamid Karzai and U.S. commanders.
He told reporters en route to Afghanistan that there are numerous challenges ahead as NATO prepares to hand over the country's security to the Afghans.
He said that although the transition is under way, the U.S. and allies must remain focused on the mission because "we are still at war."
Hagel made four trips to Afghanistan during his two terms as Nebraska senator. This is his first as Pentagon chief. He was confirmed by the Senate last week after a bruising confirmation fight.