The Trump administration is planning to withdraw thousands of troops from Afghanistan, US media say.
Reports, citing unnamed officials, say about 7,000 troops – roughly half the remaining US military presence in the country – could go home within months.
The reports come a day after the president announced the country’s military withdrawal from Syria.
Earlier on Thursday, Mr Trump’s defence secretary, Jim Mattis, announced his resignation from his post.
In his letter of departure, Gen Mattis strongly hinted at policy differences with the president, but did not cite troop withdrawals directly.
Before his election, Mr Trump repeatedly publicly advocated leaving Afghanistan, but last year he indicated he would keep boots on the ground indefinitely to prevent the country’s collapse amid a Taliban resurgence.
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Reports about the sharp reduction of forces emerged on Thursday, but have not been confirmed by US defence officials.
Afghan officials have insisted they are not concerned about the withdrawal.
“The fact that a few thousand foreign troops whose roles are primarily advisory and technical support will exit from Afghanistan will not have an impact on security situation,” presidential spokesman Harun Chukhansori told the BBC’s Afghan service.
He added that “Afghan security forces have had full responsibility of security affairs” since 2014.
However, US military reports suggest that Taliban control large swathes of Afghanistan – while a BBC study in January found that Taliban fighters were openly active in 70% of the country.
What is the story of the US in Afghanistan?
The US has been in Afghanistan since 2001, after the 11 September attacks – the longest war in US history.
When the Taliban, who controlled Afghanistan, refused to hand over al-Qaeda leader Osama Bin Laden – who had claimed responsibility for the attack – then US President George W Bush launched a military operation to find Bin Laden and remove the Taliban from power.
US special forces eventually found and killed Bin Laden in Pakistan in 2011. American-led combat operations in Afghanistan officially ended in 2014.
But in the years since then, the Taliban’s power and reach have soared – and US troops have stayed on the ground in an effort to stabilise the country.
In September 2017 Mr Trump announced the US would send 3,000 extra troops to the country, which was a clear shift from his previous rhetoric.
What has reaction been?
The Washington Post reports the potential move is being met with opposition by some of Mr Trump’s senior cabinet officials, including outgoing White House Chief of Staff John Kelly and White House national security adviser John Bolton.
Republican senator Lindsey Graham said the withdrawal could pave the way towards “a second 9/11”.
“The conditions in Afghanistan make American troop withdrawals a high risk strategy,” he said on Twitter. “We are setting in motion the loss of all our gains.”
Is this why Gen Mattis quit?
It’s hard to say.
The possibility of withdrawing from Afghanistan could have been a factor but the Syria withdrawal was likely to have been the “main trigger”, said Michael Kugelman, Deputy Director of the Asia Program at the Wilson Centre.
However, the general’s departure is likely to have an impact on the Trump administration’s Afghan policy going forward.
“He’s one of the only remaining senior officials in the administration who supports a continued US military presence in Afghanistan,” said Mr Kugelman.
“Now that [Gen] Mattis is on his way out, Trump will face even less resistance in his decision to withdraw troops.”
What is violence like in Afghanistan now?
Taliban control over Afghanistan has increased in recent months, according to a report by the US Special Inspector General for Afghan Reconstruction (Sigar).
In a quarterly report, Sigar said that the Afghan government currently controls or influences only 55.5% of the country’s districts – the lowest level recorded since it began tracking the data in 2015.
Mr Kugelman said that violence in Afghanistan had reached “alarming levels”.
“The rising levels of violence can be attributed to intensified Taliban violence… and to increasingly beleaguered Afghan security forces,” he said.
Conflict in Afghanistan goes all the way back to the 1970s. In 1979, the Soviet Union invaded Afghanistan and when it eventually withdrew, Afghanistan was in ruins, with over one million civilians killed.
This set the stage for the Taliban’s eventual takeover of the country. Now, militants and Afghan forces come up against one another on an almost daily basis somewhere in the country.
What impact would a withdrawal have?
The impact of this could be “devastating” and could lead to “increased levels of violence and major battlefield advantages for the Taliban”.
“[It] would be a soaring propaganda victory for the Taliban, as it could boast that it managed to expel US troops even without a peace deal,” said Mr Kugelman.
“It [would also] be a major psychological blow for Afghan forces. They have struggled mightily and [this] would be quite demoralising.”
But for many who support a withdrawal, it would be the end to America’s most protracted conflict on foreign soil, which has claimed more than 2,300 American lives since it began.