Hundreds of people gather outside the international airport in Kabul, Afghanistan, Tuesday, Aug. 17, 2021. (Photo: AP)

NATO secretary general Jens Stoltenberg said Tuesday the alliance had been surprised by the speed of the Taliban victory in Afghanistan but blamed Afghan leaders for the "tragedy".

"Ultimately, the Afghan political leadership failed to stand up to the Taliban and to achieve the peaceful solution that Afghans desperately wanted," he said.

"This failure of the Afghan leadership led to the tragedy we are witnessing today."