The Donald Trump administration formally initiated a partial withdrawal of US forces from Afghanistan and Iraq on Tuesday.
“By January 15, 2021, our forces, their size in Afghanistan, will be 2,500 troops,” Acting Defence Secretary Christopher Miller told reporters.
“Our force size in Iraq will also be 2,500 by that same date.” There are currently some 4,500 US troops in Afghanistan and another 3,000 in Iraq.
The Pentagon has issued a notice to commanders – known as a 'warning order' – to begin planning the downscaling of US soldiers to 2,500 each in Afghanistan and Iraq by January 15, officials told CNN.
Mitch McConnell, the Republican Senate majority leader, pushed back on Mr Trump's plans on Monday and warned that a quick withdrawal of US troops from Afghanistan would "hurt our allies".
"We're playing a limited but important role in defending American national security and interests against terrorists who would like nothing more than for the most powerful force for good in the world to simply pick up our ball and go home," he told the Senate.
"There's no American who does not wish the war in Afghanistan against terrorists and their enablers had already been conclusively won," he said. "But that does not change the actual choice before us now. A rapid withdrawal of US forces from Afghanistan now would hurt our allies and delight the people who wish us harm."
Mr Trump fired his defence secretary, Mark Esper, and appointed other top Pentagon officials last week after long-standing concerns that his priorities were not being dealt with urgently enough at the defence department.
These included ending the 19-year war in Afghanistan by Christmas, an ambitious target some welcomed but which Mr Trump's critics feared could be reckless given the ongoing militant violence plaguing the country.
Afghanistan has featured in a flurry of introductory calls by acting Defence Secretary Christopher Miller, Mr Esper’s replacement, to US allies’ defence chiefs.
Speaking anonymously after the calls with allies, a US defence official suggested that Mr Trump would not push a withdrawal faster than conditions on the ground allow.
Both US and Afghan officials are worried about troubling levels of violence by Taliban insurgents and their links to Al Qaeda.
It was those ties that triggered US military intervention in 2001 following the 9/11 attacks, carried out by Al Qaeda. Thousands of US and allied troops have died fighting in Afghanistan since.
Some US military officials, citing counter-terrorism priorities in Afghanistan, have privately urged Mr Trump against a total withdrawal of US troops at this point and want to keep levels at about 4,500 for now.
"The president has acted appropriately in this, has never said: 'Hey, we're going to zero. Let's go tomorrow.' It has always been a conditions-based effort and that effort continues," a senior US defence official said.
The White House did not immediately respond to requests for comment.
'See the fight to the finish'
Over the past four years, predicting Mr Trump’s policy pronouncements has not always been easy.
On October 7, Mr Trump said on Twitter: "We should have the small remaining number of our BRAVE Men and Women serving in Afghanistan home by Christmas!"
But US officials say he has yet to issue orders to carry out any withdrawal. Doing so now would be difficult for the US military to execute, especially given the reliance of Nato allies on the US for logistical support, sources said.
One Nato official, who asked not to be identified, said the belief was the US could soon announce a drawdown to 2,500-3,000 troops by Christmas.
National security adviser Robert O’Brien already raised such a possibility, saying last month the US presence in the region would be reduced to 2,500 by early 2021.
A Nato diplomat said Mr Miller, the newly appointed Pentagon chief, in his introductory call with Nato Secretary General Jens Stoltenberg, did not suggest a complete withdrawal but instead a reduction of troops.
The senior US defence official said US withdrawals from Afghanistan had been carried out in an “educated way so as not to revisit the Iraq withdrawal that failed in 2011”.
Barack Obama, who was then the president, withdrew troops against military advice, only to return them to Iraq three years later.
Taliban militants, fighting against the US-backed government in Kabul, have called on the US to stick to a February agreement with the Trump administration to withdraw troops by May, subject to certain security guarantees.
Violence has been rising throughout Afghanistan, with the Taliban attacking provincial capitals, in some case prompting US air strikes.
In Kabul, there is growing fear of a precipitous withdrawal that could further embolden the Taliban and undercut difficult peace talks, sources told Reuters.
Mr Miller said on Saturday that he could accelerate the withdrawal of US troops from Afghanistan and the Middle East, but he did not offer a timetable and stressed the need to finish the fight against Al Qaeda.
The Taliban harboured Al Qaeda’s leaders and the US special envoy for Afghanistan said it had not fulfilled the February accord commitment to break ties with Al Qaeda.
“We are on the verge of defeating Al Qaeda and its associates, but we must avoid our past strategic error of failing to see the fight through to the finish,” said Mr Miller, a former Green Beret and counter-terrorism official.