NATO: Taliban mustn't let terrorism gain foothold

"Those now taking power have the responsibility to ensure that international terrorists do not regain foothold," Stoltenberg told a news conference, adding that members of the military alliance have the capacity to respond to future threats.

Jens Stoltenberg also told the news conference that the speed of the collapse of the Afghan National Army in the face of the Taliban's advance was a surprise.

"Ultimately the Afghan political leadership failed to stand up the Taliban and to achieve the peaceful solution that Afghans desperately wanted," the former Norwegian prime minister said, adding the take-over of Kabul by the group was a 'tragedy.'

Stoltenberg called on the Taliban on Tuesday (August 17) to facilitate the departure of all those who want to leave Afghanistan.