According to sources cited by several U.S.-based media outlets, President Trump took the decision on Tuesday, the same day he decided to pull the troops out of Syria because in his words, "the Islamic State (IS) had already been defeated."
As a result, Defense Secretary James Mattis announced his resignation on Thursday over significant policy differences with the president. Mattis had argued for maintaining a strong U.S. military presence in Afghanistan to bolster diplomatic peace efforts.
According to CNN, Trump made the decision thinking about the State of the Union speech, which might take place between January and February.
The U.S. currently has about 14,000 troops fighting a 17-year-old war in Afghanistan, with tasks ranging from military and security advice to counterterrorism missions against Al Qaeda and the IS. According to the New York Times, such move will force local security forces to be “more reliant on their own troops and not Western support.”
U.S. airstrikes in Afghanistan are at its height as ground troops are struggling to defend the territory from Taliban forces and other groups.
More than 2,400 Afghan troops have been killed since the U.S. and NATO formally ended military operations in 2014.
U.S. officials are currently engaged in talks with the Taliban, who now control a significant amount of territory. The Taliban insurgency has strengthened its grip over the past three years, with the government in Kabul controlling just 56 percent of Afghanistan, down from 72 percent in 2015, a U.S. government report showed.
Trump privately has been grousing about U.S. military involvement in Afghanistan, telling an ally as recently as Wednesday words to the effect of, "What are we doing there? We've been there all these years."
One of the sources, who asked to remain unidentified, said it appeared the president "has lost all patience" with the U.S. military presence in Afghanistan.
Republican Senator Lindsey Graham, often a vocal Trump ally, warned of possible danger to the United States if the drawdown goes through.
"The conditions in Afghanistan - at the present moment - make American troop withdrawals a high risk strategy. If we continue on our present course we are setting in motion the loss of all our gains and paving the way toward a second 9/11," Graham said in a statement.
Trump last year approved an increase in U.S. troops but acknowledged that he did so reluctantly.
Late last month, at least 22 Afghan police were killed in a Taliban ambush in Afghanistan's western province of Farah, adding to the growing casualty toll on Afghan security forces.
Earlier this week, U.S. special envoy Zalmay Khalilzad and Taliban representatives held talks in Abu Dhabi on a deal that would end the war. Officials from Saudi Arabia and the United Arab Emirates also took part.
The Saudi ambassador to Washington, Khalid bin Salman, tweeted on Thursday that the discussions had been productive and would bring "very positive results by the beginning of next year."
But a former senior State Department official familiar with the issue said that the Taliban representatives rejected a proposal by Khalilzad for a ceasefire and demanded that the talks focus on a U.S. withdrawal.
Trump has been critical of the U.S. military intervention in Afghanistan citing domestic reasons. During his presidential campaign, he promised to stay out of international conflicts and focus on U.S. citizens’ well being.
In 2011, he asked "when will we stop wasting our money on rebuilding Afghanistan? We must rebuild our country first."
In an interview with The Washington Post in November, Trump said troops continued in Afghanistan because every expert he spoke with told him that if they didn’t remain over there, they would be fighting in the U.S.
The United States went to war in Afghanistan in 2001 in the wake of the Sept. 11, 2001 attacks on the World Trade Center and the Pentagon, seeking to oust the Taliban militants harboring Saudi-raised militant Osama bin Laden, who led plans to carry out the attacks.