Trump to withdraw thousands of troops from Afghanistan in major boost for Taliban

US President Donald Trump has decided to pull a significant number of troops from Afghanistan, a US official told AFP on Thursday, with the Afghan presidency brushing off concerns the drawdown would affect security.

Reports suggested as many as half of the 14,000 troops in the war-torn nation could be leaving.

The surprise move stunned and dismayed foreign diplomats and officials in Kabul who are involved in an intensifying push to end the 17-year conflict with the Taliban, which already controls vast amounts of territory and is causing "unsustainable" Afghan troop casualties.

"If you're the Taliban, Christmas has come early," a senior foreign official in the Afghan capital told AFP on the condition of anonymity.

"Would you be thinking of a ceasefire if your main opponent has just withdrawn half their troops?"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 by AFP. 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. 

But a spokesman for Afghan President Ashraf Ghani downplayed the effect of any pull-out.

"If they withdraw from Afghanistan it will not have a security impact because in the last four and half years the Afghans have been in full control," presidential spokesman Haroon Chakhansuri said via social media.

US-led NATO combat troops withdrew from Afghanistan at the end of 2014, handing responsibility for securing the country to local forces. 

Trump's decision apparently came Tuesday as Khalilzad met with the Taliban in Abu Dhabi, part of efforts to bring the militants to the negotiating table with the Afghan government.

They discussed issues ranging from the group's longstanding demand for a pull-out of foreign troops, the release of prisoners including Anas Haqqani, son of the Haqqani network's founder, and a ceasefire, Khalilzad told Afghan media in Kabul on Thursday.

"That decision has been made. There will be a significant withdrawal," the American official told AFP on condition of anonymity.

Tuesday was also the day Trump told the Pentagon he wanted to pull all US forces out of Syria. Defence Secretary Jim Mattis quit Thursday, saying his views were no longer reconcilable with Trump's.

'Tremendous' advantage

Critics suggest the president's twin foreign policy decisions on Syria and Afghanistan could unspool a series of cascading and unpredictable events across the Middle East and in Afghanistan.

US Senator Lindsey Graham described the Afghanistan decision as 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," he warned via Twitter. 

Afghan forces have been taking what experts describe as "unsustainable" casualties since NATO pulled its combat forces out of Afghanistan at the end of 2014.

Lieutenant General Kenneth McKenzie, who has been nominated to lead the US military's Central Command, warned earlier this month that unless recruiting and training improve, local forces will not overcome the current casualty rate.

The United States has about 14,000 troops in Afghanistan working either with a NATO mission to support Afghan forces or in separate counter-terrorism operations. 

The Wall Street Journal and the New York Times reported that more than 7,000 troops would be returning from Afghanistan.

The Taliban was toppled from power by a US-led invasion in 2001 following the 9/11 attacks masterminded by Al-Qaeda leader Osama bin Laden, who had been harboured by Afghanistan.

The war is now America's longest, with more than 2,200 US military personnel killed there since the start 2001, including 13 this year.

Mattis and other top military advisors last year persuaded Trump to commit thousands more troops to Afghanistan as part of a strategy that also included ramping up airstrikes on the Taliban and its relatively small but potent rival, the Islamic State group. 

Trump at the time said his instinct was to get out of Afghanistan.

Khalilzad, who has met with Taliban representatives several times in recent months, has expressed hopes for a peace deal before the Afghan presidential elections scheduled for April.

Foreign observers and officials said Trump's move had handed the Taliban a major propaganda and tactical victory, without the militants having to make any concessions.

"It's gotten the troop withdrawals it's always wanted without even having to make any concessions, much less reach a deal," Michael Kugelman of the Wilson Center told AFP. 

"Now it has a tremendous battlefield advantage, which gives it the opportunity to scale up its fight in a huge way."