President Donald Trump has decided to pull a significant number of troops from Afghanistan, US officials told US media, a day after he announced a withdrawal from Syria.
"That decision has been made. There will be a significant withdrawal," one official told AFP on condition of anonymity.
The US has about 14,000 troops in Afghanistan working either with a NATO mission to support Afghan forces or in separate counter-terrorism operations. The New York Times and Wall Street Journal reported that around half that number will be withdrawn.
Mr Trump made his decision on Tuesday, the same time he told the Pentagon he wanted to pull all US forces out of Syria.
Defence Secretary Jim Mattis quit earlier on Thursday, saying his views were no longer reconcilable with Trump's.
The president's twin foreign policy decisions on Syria and Afghanistan could unleash a series of cascading and unpredictable events across the Middle East and Afghanistan.
Mr Mattis and other top military advisers last year persuaded Trump to commit thousands of new troops to Afghanistan, where the Taliban were slaughtering local forces in the thousands and making major gains.
Mr Trump at the time said his instinct was to get out of Afghanistan.
The pull out comes as the US pushes for a peace deal with the Taliban and following indirect talks between Afghan government officials and Taliban representatives in Abu Dhabi where potential confidence-building measures were discussed.
The move stunned and dismayed diplomats and officials in Kabul who are intensifying a push to end the 17-year conflict with the Taliban.
"If you're the Taliban, Christmas has come early," a senior foreign official in the Afghan capital told AFP.
"Would you be thinking of a ceasefire if your main opponent has just withdrawn half their troops?"
Taliban spokesman Zabiullah Mujahid would not comment about the troop withdrawal when contacted. But a senior Taliban commander welcomed the decision.
"Frankly speaking we weren't expecting that immediate US response," the official told AFP from an unknown location in northwest Pakistan.
"We are more than happy, they realised the truth. We are expecting more good news."
It is not clear if US peace envoy Zalmay Khalilzad or the Afghan government had been warned of Trump's plans in advance.
Haroon Chakhansuri, a spokesman for Afghan President Ashraf Ghani, downplayed the news. "It will not have a security impact because in the last four and half years the Afghans have been in full control," he said.