Al-Qaeda has re-established training camps in Afghanistan and is once again a major threat to the UK, counter-terror sources fear.
It has secretly set up small bases in the war-torn country and is preparing fighters amid the chaos.
Several thousand are now thought to be living there, many of them helped by the Afghan Taliban.
Sources said the US intelligence agency the CIA is trying to tackle the threat using drones.
The US military is believed to have blasted one of al-Qaeda’s new bases days after killing the terror group’s leader Ayman Zawahiri as he stood on a balcony in Kabul.
The site in Ghazni, south west of the capital, was an old US military base, probably taken over by al-Qaeda.
A western military source said: “This suspected drone attack, coming so soon after Zawahiri was targeted, is indicative of a new era in the fight against terror.
“It is likely this was a terrorist training camp. Zawahiri’s presence in Kabul was confirmation that al-Qaeda has been re-establishing a footprint in Afghanistan for quite some time.
“But it is very likely that there are more such training camps and very likely they are in positions where coalition troops had once had camps.”
Labour MP John Spellar, vice chairman of the Parliamentary Defence Committee said: “It’s clear the Taliban leadership in Afghanistan has reneged on its promise to not harbour al-Qaeda.
“And it is right to take action to prevent al-Qaeda once again being able to pose a threat to lives and liberty around the world.”
An R9X Hellfire missile, modified with spring-out blades to minimise collateral damage, is thought to have killed Zawahiri, 71, on July 31.
The Mirror understands several members of the terrorist Haqqani family also died. The US claims no civilians were killed.
It is believed a hard core of the Haqqani leadership fled Afghanistan soon after.
The US’s suspected “over the horizon” drone programme means its spies are concerned about the rise of al-Qaeda in Afghanistan.
America is the terror group’s No1 target with the UK a close second.
It is also believed Islamic State in the Khorasan, the local franchise of the group, has close to 10,000 fighters in Afghanistan.
They have frequently battled the country’s Taliban rulers, sparking violent tension in the country.
Colonel Richard Kemp, who commanded troops in Afghanistan, said: “I have little doubt there are al-Qaeda training camps in Afghanistan and these are an obvious danger.”
Former intelligence officer Mike Tapp added: “Allowing al-Qaeda freedom of movement affords them the opportunity to train and operate, which will undoubtedly increase the risk to the West, including in the UK, where some of its operatives may be residing.”
