NATO will likely join the United States in withdrawing all troops from Afghanistan in September, German Defence Minister Annegret Kramp-Karrenbauer said Wednesday.

"We always said: we'll go in together, we'll leave together," she told ARD public television. "I am for an orderly withdrawal and that is why I assume that we (NATO) will agree to that today."

NATO defence and foreign ministers will hold a video conference Wednesday after the US said it was planning to withdraw its forces from Afghanistan by the 20th anniversary of the September 11 suicide hijackings this year.

A US official said on Tuesday that President Joe Biden had reached the conclusion to end Washington's two-decade involvement in Afghanistan by late this year. 

The US has some 2,500 troops in Afghanistan as part of a 9,600-strong NATO mission in the country.

NATO allies including Germany had been waiting for Biden to decide whether the US would stick to a May 1 deadline to withdraw under a deal struck between the administration of former US leader Donald Trump and the Taliban. 

Kramp-Karrenbauer said it was now important "for us in NATO to synchronise our planning with the US planning". She did not give a precise date when German troops would withdrawal from the strife-racked country.