The Taliban must not let Afghanistan become a breeding ground for terrorism again, NATO said on Tuesday, warning that the alliance retained the military power to strike any terrorist group from a distance.

"Those now taking power have the responsibility to ensure that international terrorists do not regain a foothold," NATO Secretary-General Jens Stoltenberg told reporters in Brussels.

"We have the capabilities to strike terrorist groups from a distance if we see that terrorist groups again try to establish themselves and plan, organise attacks against NATO allies and their countries," he added.

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The fight against the militant Al Qaeda organisation, that was responsible for the 9/11 attacks and whose leadership was hosted by the Taliban, was the main reason for the West to intervene in Afghanistan in 2001.

As NATO this summer completed military operations after almost two decades, the Taliban rapidly advanced, capturing the biggest cities in days rather than the months predicted by US intelligence.

The sudden takeover of the capital Kabul caused thousands of people to flee to the city's airport, which is still being held by the US military, desperate to get on evacuation flights.

Stoltenberg called on the Taliban to facilitate the departure of all those who want to leave the country, and said that Western defence allies had agreed to send more evacuation planes to Kabul.