US Army General Austin Scott Miller assumed command of the 41-nation NATO mission in Afghanistan from General John Nicholson, who held the post for more than two years.
US Army General Scott Miller assumed command of NATO forces in Afghanistan on Sunday, arriving as Washington faces growing questions over its strategy to force the Taliban into talks to end the 17-year conflict.
Miller, former commander of the US military's Joint Special Operations Command, takes over at a time of mixed hope and fear for the Western-backed government in Kabul.
"To be successful, we must continually learn and adapt to the enemy and the environment," Miller said at a change of command ceremony at the headquarters of the NATO-led Resolute Support mission in Kabul.
"There is no room for status quo. We cannot afford to be complacent."
The United States is now a year into its strategy of stepping up pressure on the Taliban by increasing airstrikes and sending thousands more troops to train and advise Afghan forces, but clear signs of success have so far proved elusive.
Civilian casualties are running at record levels, there have been repeated attacks on major cities such as Kabul and Jalalabad and while the Taliban have not managed to take any major urban centres, they control large areas of the countryside.
In June, a report by the Pentagon's Lead Inspector General offered a downbeat view, saying there was little publicly available evidence that "actions to increase pressure on the Taliban were having a significant impact."
Afghan forces, meanwhile, are chronically understrength because of heavy casualties and high levels of desertion, and continue to face problems with organisation and logistics that have long hampered their effectiveness.
Hopes of a breakthrough in achieving peace talks were raised by an unprecedented ceasefire over the Eid holiday in June but optimism was dampened by the insurgents' dramatic assault on the city of Ghazni last month.
"I believe that some of the Taliban want peace also but they are being encouraged to keep fighting," the outgoing commander Gen. John Nicholson said at the ceremony, urging the insurgents to listen to demands for peace from the Afghan people.
"It is time for this war in Afghanistan to end," he said.
Like Nicholson, Miller spent years in Afghanistan before assuming command of US and coalition forces there and his career has followed the different stages of what is now America's longest war.
He was among the first US troops to arrive in 2001 as part of the campaign to topple the Taliban following the Sept. 11 attacks in the United States.
Almost a decade later, he served during the "surge" ordered by President Barack Obama, which saw more than 100,000 NATO troops in Afghanistan in a bid to crush the insurgency, as well as in 2013-14 as most international troops were withdrawn.
Washington has accepted that a purely military victory is not possible and has focused on forcing the Taliban to the negotiating table.
But increasingly questions are being asked about whether the strategy is working amid reports that President Donald Trump has grown impatient with the lack of clear progress.