Western intelligence chiefs are worried. They have good reason to be.

The hurried departure this month of the remaining Western forces from Afghanistan, decreed by US President Joe Biden, has emboldened Taliban insurgents.

In recent days they have seized one district after another, overrunning bases where demoralised government troops have often surrendered or fled.

Now, say observers, the spectre of international terrorism is making an unwelcome return.

"The Biden withdrawal from Afghanistan makes a Taliban takeover inevitable and gives al-Qaeda the opportunity to rebuild its network, to the point where it could once again plot attacks around the world," Dr Sajjan Gohel, a security and terrorism analyst, told the BBC.