US on alert after ‘credible but unconfirmed’ threat of anniversary attack by al-Qaeda

counter-terror officials in the US have warned of a credible but unconfirmed threat by al-Qaeda to use a car bomb on bridges or tunnels in New York or Washington.

It was the first word of an “active plot” timed to coincide with the sombre commemoration of the terror group’s 11 September attacks a decade ago that killed nearly 3,000 people.

Police in both cities said they would increase their already increased staffing levels in the light of the new intelligence.

Law enforcement officials were pursuing three people who may be travelling to the US or who recently entered the country, based on detailed information received by the intelligence community late on Wednesday, officials said.

US vice-president Joe Biden said there was no confirmation anyone had travelled into the US for such a plot, but the tip had come from a credible source.

“There’s no certitude,” Mr Biden said. “The thing we are all most worried about is what they call a ‘lone ranger’, a lone actor, not some extremely complicated plan like it took to take down the World Trade towers.”

The threat had come in a single piece of information and was so specific – and came at such a time of already heightened alert – that it could not be ignored, officials said.

“There is specific, credible but unconfirmed threat information,” the head of the FBI’s New York division, Janice Fedarcyk, said. “As we always do before important dates like the anniversary of 9/11, we will undoubtedly get more reporting in the coming days.”

New York mayor Michael Bloomberg took a trip on the subway yesterday to assure commuters that the city was fully prepared for a potential terror threat before the anniversary, while police commissioner Raymond Kelly said officers were beefing up security at bridges and tunnels, setting up vehicle checkpoints, doing bomb sweeps of parking garages, and towing away more illegally parked cars.

Commuters were told to expect a show of force at two main railway stations, Grand Central and Pennsylvania, and at the Times Square subway station.

The Port Authority of New York and New Jersey, which owns the trade centre site, was also at a heightened state of alert.

A spokesman said there would be increased vehicle checks at every crossing, a greater police presence at all facilities, and more bag checks at airports, and bus and rail terminals.

In Washington, police chief Cathy Lanier said officers would work 12-hour shifts over the next few days. She said scheduling changes were “part of our plan” and that “maintaining a certain sense of unpredictability is essential to the success of any security plan”.

A US official said the source of the terror tip indicated that al-Qaeda’s new leader, Ayman al-Zawahri, had been involved in planning the plot. In addition, information gleaned from Osama bin Laden’s compound in Pakistan after he was killed indicated al-Qaeda had considered attacking the US on this anniversary.