Newly appointed US Acting Secretary of Defence Christopher Miller told the military that all wars must end and it is time to come home, according to a memorandum issued by the Pentagon.
"All wars must end. Ending wars requires compromise and partnership. We met the challenge: we gave it our all. Now, it's time to come home," Xinhua news agency quoted Miller as saying on Saturday in his first message to all employees of the Department of Defence.
The acting Pentagon chief also said that the US remains committed to ending the war against Al Qaeda since 2001 and is "on the verge of defeating" the terrorist group.
"This fight has been long, our sacrifices have been enormous, and many are weary of war - I'm one for them," he said.
"But this is the critical phase in which we transition our efforts from a leadership to supporting role."
The war in Afghanistan, which has caused about 2,400 US military fatalities, is the longest one in American history.
Miller, a US special forces veteran who fought in this war, was appointed by President Donald Trump on November 9 as Acting secretary of Defence to replace former Pentagon chief Mark Esper.
The message indicated that he might accelerate the pace to pull US troops out of Afghanistan.
Currently, there are around 4,500 US troops in the country.
Trump has long sought a full withdrawal from Afghanistan, but some of his senior aides from the military and the Pentagon suggested a condition-based withdrawal, a more cautious approach.
Trump previously tweeted that he wanted troops returning home by Christmas.
His National Security Adviser Robert O'Brien later noted that Trump's tweet was only an expression of desire, saying US troops in Afghanistan would be reduced to 2,500 level by early 2021.
The US and Taliban signed an agreement in late February, which called for a full withdrawal of the American military forces from Afghanistan by May 2021 if the militant group meets the conditions of the deal, including severing ties with terrorist groups.
But Commander of US Central Command Kenneth McKenzie said that the Taliban "had not shown conclusively that they're going to break with Al Qaeda".