U.S. Army General Scott Miller has assumed command of NATO forces in Afghanistan as Washington faces growing questions over its strategy to force the Taliban into peace talks with 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 on September 2.
"There is no room for status quo. We cannot afford to be complacent," Miller said.
The United States is now a year into its strategy of stepping up pressure on the Taliban by increasing air strikes and sending thousands more troops to train and advise Afghan forces.
However, there is no clear signs of success so far, as militants continue to attack government and military targets and civilian casualties are running at record levels.
Afghan forces, meanwhile, are understrength because of heavy casualties and high levels of desertion and continue to face problems with organization and logistics.
While the Taliban has not managed to take any major urban centers, it controls large areas of the countryside.
Speaking at the ceremony in Kabul, the outgoing commander, General John Nicholson, urged militants to listen to demands of peace from the Afghan people.
"I believe that some of the Taliban want peace also, but they are being encouraged to keep fighting," he said. "It is time for this war in Afghanistan to end."
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."
An unprecedented cease-fire over the Eid holiday in June raised hopes for a breakthrough in achieving peace talks. However, optimism was dampened by the Taliban's assault on the city of Ghazni in July.
Miller commands some 16,000 NATO troops -- including about 14,000 U.S. forces -- under the Resolute Support mission that is focused on training, advising, and assisting Afghan forces.
On the eve of the change-of-command ceremony, NATO Secretary-General Jens Stoltenberg tweeted that "NATO remains committed to supporting Afghan security forces as they create the condition for lasting security and peace."
Afghan national security adviser Hamdullah Mohib, who attended the ceremony said, "Together we will eliminate the menace of terrorism from Afghanistan and the region."
Mohib, who had been ambassador to Washington, was named by Afghan President Ashraf Ghani to his post on August 25, replacing Mohammad Hanif Atmar, who had resigned.
Atmar's departure, reportedly because of policy differences with Ghani, raised concerns about stability among the Afghan security services. Three other senior security officials also offered their resignations, but they were rejected by the president.
He asked Atmar for his support to show "continuation...not just on the American side but on ours as well."
Potentially easing some concerns, Mohib praised Atmar, who was also at the ceremony, saying, "Yours are difficult shoes to fill."
The first U.S. troops arrived in Afghanistan in 2001 as part of a campaign to topple the Taliban following the September 11 terrorist attacks in the United States.
Former U.S. President Barack Obama announced an additional 30,000 troops in 2009 and by 2011 there were 100,000 U.S. troops in Afghanistan.
The NATO combat mission, which numbered more than 130,000 in 2011, ended in December 2014.