"NATO Allies decided in mid-April to start the withdrawal of Resolute Support Mission forces by May 1 and this withdrawal has begun. This will be an orderly, coordinated, and deliberate process," a NATO official told AFP.

Members of the US-backed alliance agreed this month to wrap up their 9,600-strong mission in Afghanistan after Biden made the call to end Washington's longest war.

The decision -- which delayed by several months a deadline agreed by former US leader Donald Trump -- came despite fears it could allow the Taliban to regain power in the country.

The NATO official said the safety of the alliance's troops "will be a top priority every step of the way, and we are taking all necessary measures to keep our personnel from harm".

"Any Taliban attacks during the withdrawal will be met with a forceful response. We plan to have our withdrawal completed within a few months," the official said, refusing to give any further details on the timeline.

Biden said the US withdrawal would be completed by September 11, the twentieth anniversary of the 9/11 attacks on America that sparked its military involvement in Afghanistan.

Germany's defence ministry has said it plans to get its 1,300 troops out of the country by early July.

NATO's training and support mission, which includes some 2,500 US troops and relies heavily on Washington's military assets, has personnel from 36 alliance member nations and partner countries.

The US has said it is temporarily deploying extra troops to protect international forces as they withdraw and has prolonged the presence of an aircraft carrier in the region to support the pull-out.