US intelligence chiefs held a White House summit yesterday to discuss a classified report that concluded that al-Qaeda is now stronger than at any time since September 11, 2001.

Details of the five-page document, entitled “Al-Qaeda better positioned to strike the West”, were leaked amid growing signs that America is nervous about the prospect of another terrorist attack. There was particular concern that Europeans could be used to launch such operations.

Michael Chertoff, the Homeland Security Secretary, has spent days trying to play down comments that his “gut feeling” was that the US faced a heightened risk of attack this summer.

Yesterday a flight from Los Angeles to London was diverted to New York after a crew member became suspicious of one of the passengers, who had been seen bypassing security by travelling on an employee-only bus.

Mr Chertoff emphasised yesterday that “we don’t have any specific information about an imminent or near-term attack on the homeland”. However, The Times has been told that US and British intelligence services monitoring al-Qaeda networks have picked up “an increased level of chatter” in recent weeks.

The US is evaluating information gleaned from the recent thwarted terror plots in Britain, including that two of the suspects had applied to practise medicine in Philadelphia.

The intelligence report compiled by the National Counterterrorism Centre is believed to state that al-Qaeda is “showing greater and greater ability to plan attacks in Europe and the United States”. It adds that the network is “considerably operationally stronger than a year ago” and has “regrouped to an extent not seen since 2001”.

Fresh claims emerged yesterday that agents had been given two weeks to track down 700 people on an official FBI “worry list”. One group that they are known to be concerned about consists of radical British Muslims who may have made contact with al-Qaeda groups in Pakistan before travelling to the US on the visa-waiver programme.

Mr Chertoff said yesterday: “Something I’ve said repeatedly . . . is we have to watch Europe because the growth of home-grown terrorism over there creates a vulnerability for those who might use Europe as a platform into the United States.”

Intelligence analysts told Congress yesterday that al-Qaeda’s training activities, funding and communications have increased as the militant network has settled into new bases in remote areas of Pakistan. Al-Qaeda’s central command was “resurgent” in planning operations, John Kringen, head of the CIA’s intelligence directorate, said. “They seem to be fairly well settled into the safe haven in the ungoverned spaces of Pakistan. We see more training. We see more money. We see more communications.”

The White House is wary of over-emphasising the threat because that would undermine President Bush’s claim that “we’re winning – al-Qaeda is on the run”, when the US is having to admit only patchy progress in Iraq.

“There is a perception in the coverage [of the intelligence report] that al-Qaeda may be as strong today as they were prior to September 11,” Mr Bush said at a White House press conference yesterday. “That is simply not the case. The report will say ‘since September 11’. Because of the action we have taken, al-Qaeda is weaker today than they would have been. They are still a threat and they are still dangerous. That is why it is important we succeed in Iraq and Afghanistan.”

Mr Chertoff said: “The enemy continues to try to improve itself and rebuild itself. We’ve clearly done a lot of damage to al-Qaeda, we’ve killed or captured a lot of the senior leadership. They try to reconstitute themselves. They have found some places in Pakistan and other parts of the world where they can begin the process of training . . . But I do think the level of intent on the part of the enemy remains very high.”

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