Army General Scott Miller has assumed command of US and NATO forces in Afghanistan, arriving as Washington faces growing questions over its strategy to force the Taliban into talks to end the 17-year conflict.

Miller, the 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 on Sunday 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 US is now a year into its strategy of stepping up pressure on the Taliban by increasing air raids and sending thousands more troops to train and advise Afghan forces, but clear signs of success have so far proven 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 has 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 understaffed because of heavy casualties and high levels of desertion, and continue to face the 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 fighters’ 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,” General John Nicholson, the outgoing commander, said at the ceremony.

“It is time for this war in Afghanistan to end,” he said.