President Donald Trump is planning to withdraw more than 5000 of the 14,000 US troops in Afghanistan, a US official says, in the latest sign Trump's patience is thinning with America's longest war and overseas military interventions.
On Wednesday, Trump rebuffed top advisers and decided to pull all US troops out of Syria, a decision that contributed to US Defense Secretary Jim Mattis abruptly quitting on Thursday over significant policy differences with the president.
One official, speaking on the condition of anonymity, said a decision had been made and verbal orders had been given to start planning for the drawdown.
The official said timelines were being discussed but it could happen in weeks or months.
It's unclear how the United States with less than 9000 forces in Afghanistan will be able to fulfil the full set of missions now underway, including training Afghan forces, advising them in the field, and waging an air campaign against the Taliban and other militant groups.
Instead, the United States almost certainly would have to curtain its missions, something that could provide an opportunity for a resurgent Taliban to expand their offensives across Afghanistan.
Mattis had argued for maintaining a strong US military presence in Afghanistan to bolster diplomatic peace efforts. He resigned shortly after US officials raised the possibility that Trump would order the drawdown.
The decision on Syria has bewildered US allies and triggered harsh reaction from Trump's fellow Republicans in Congress.
The Pentagon declined to comment on Afghanistan.
Garrett Marquis, a spokesman for the National Security Council, said the White House would not comment "on future strategic developments".
The United States went to war in Afghanistan in 2001 after the September 11, 2001, attacks on the World Trade Center and the Pentagon, seeking to oust the Taliban militants harbouring Saudi-raised militant Osama bin Laden, who led plans to carry out the attacks.
US officials are engaged in talks with the Taliban, who now control a significant amount of territory.
The Taliban insurgency has strengthened its grip in the past three years, with the government in Kabul controlling just 56 per cent of Afghanistan, down from 72 per cent in 2015, according to a US government report.
Trump privately has been grousing about US 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."
More than 2400 US forces have died in the 17-year-old war in Afghanistan and Pentagon officials have repeatedly warned a precipitous exit would allow militants to develop new plots on America.
Republican Senator Lindsey Graham, often a vocal Trump ally, warned of possible danger to the United States if the drawdown goes through, calling it a "high-risk strategy".
Trump last year approved an increase in US troops but acknowledged he did so reluctantly.
