US President Joe Biden is set to announce the withdrawal of all US troops from Afghanistan by September 11, an official told reporters on condition of anonymity on Tuesday.

The symbolic date, 20 years to the day of the historic terrorist attack on the World Trade Center in New York, will end the longest war in the US history.

The Trump administration had set the pullout date for May 1. Biden's decision will delay the end of the war by another five months.

Following the news of the planned withdrawal, NATO members set up a video conference for Wednesday, an alliance official told AFP. The military alliance has 9,600 personnel in the country, of which some 2,500 are US troops.

Just hours after Biden's announcement, a spokesman for the Taliban said the militant group would not attend a planned summit in Turkey until all foreign troops leave the country.

"Until all foreign forces completely withdraw from our homeland, [we] will not participate in any conference that shall make decisions about Afghanistan," Mohammad Naeem, spokesman for the Taliban office in Qatar, wrote on Twitter.

Kabul expected to 'struggle' without US help

The military withdrawal will not depend on the situation on the ground — despite fears that the Taliban could make major gains.

"The president has judged that a conditions-based approach, which has been the approach of the past two decades, is a recipe for staying in Afghanistan forever," the official said.

The latest delay was largely for logistical reasons, and the new date was coordinated with allies.

US intelligence also released a report that found that Afghanistan's government would "struggle" to stand its ground against the "confident" Taliban.

Afghanistan has been gripped by violent attacks, targeted assassinations and car bombs over the past year. Three civilians were killed by a suicide car bomb in the north of the country on Tuesday.

The official said US forces had warned the Taliban against carrying out attacks on troops as they prepare to leave the country.

"We have communicated to the Taliban in no uncertain terms that, if they do conduct attacks against US or allied forces as we carry out this drawdown, that we will hit back hard," the official said.

Taliban confident of victory over government forces

Donald Trump, the president at the time, had reached an agreement with the Taliban in February 2020 to pull US troops by May 2021 as long as the group promised not to support al-Qaida and other extremists.

The Trump administration also tried to pave the way for peace negotiations between the internationally recognized Afghan government and the Taliban — although talks have since faltered.

The US national intelligence report states that the Taliban "is confident it can achieve military victory."

"Afghan forces continue to secure major cities and other government strongholds, but they remain tied down in defensive missions and have struggled to hold recaptured territory or reestablish a presence in areas abandoned in 2020," it said.

ab/dj (AP, AFP, dpa, Reuters)