U.S. 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 U.S. 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.