Western intelligence and security officials say the threat of a terror attack by militants over the holiday season is extremely high, with the greatest concern focusing on a possible plot targeting Europe.
While the year-end period is always a time of concern because of the vast number of travelers, authorities' nervousness is palpable in 2006.
A senior French counterterrorism official said that intelligence agencies throughout the continent are on "tenterhooks" and that "all of the warning lights are red," though they have yet to uncover any specific plan for attack.
"The threat is at its highest level," said the French official, who spoke on condition of anonymity because of the secretive nature of his job. "All (security) services are on tenterhooks. And it's not just us (in France). Work is underway everywhere but nothing concrete is emerging. Ends of the year are often bad. This year we haven't managed to distinguish a precise plot."
Those fears were echoed in Britain, already on edge after the failed August plot to bring down commercial jetliners over the Atlantic.
British Home Secretary John Rid said on Sunday that it was "highly likely" that terrorists would attempt to mount an attack over the holiday period when the number of travelers swells. He gave no other details.
The head of Britain's domestic spy agency, MI5, has said her agents are tracking almost 30 terrorist plots involving 1,600 suspects, and that at least five major terror plots had been thwarted since the July 2005 transit bomb attacks in London.