Jan. 25, 2008 -- Law enforcement officials throughout Europe say they are are urgently hunting for members of an al Qaeda terror cell that was allegedly planning to attack the transit system in Barcelona.
Sources tell ABC News those being sought are believed to be bomb makers and suicide killers who were working with a 14-member operation.
While it is unclear whether the Barcelona attacks were imminent, Spanish authorities say they have no doubt that the threat was serious.
The plot was allegedly developed by senior al Qaeda leaders hiding in Pakistan, with members of the cell making their way into Spain in recent days.
"Here we are looking at something different: a well-organized group who were going beyond ideological radicalism to acquiring materials to make explosives and therefore eventually to carry out violent attacks," Spanish Interior Minister Alfredo Perez Rubalcaba said at a press conference last week.
U.S. officials tell ABC News that in the wake of the thwarted attacks on Barcelona's transit system they are deeply troubled by this latest example of a reconstituted al Qaeda.
The National Intelligence Estimate released last year warned that al Qaeda was training scores of recruits in the tribal regions of Pakistan.
"If this story is true, it means that al Qaeda is alive. It has money. It has people that are trained. It has a network to send people -- large numbers of people -- out as a team and that it has the capability of striking thousands of miles from its base in Pakistan," former government counter-intelligence official and ABC News consultant Richard Clarke said of this latest incident.
The pace of plots directed or inspired by al Qaeda has been intensifying in recent months, with Europe as the focus.
Last September in Germany, three Islamic radicals were accused of targeting U.S. military installations there.
Also in September in Denmark, suspected terrorists were charged with planning a bombing campaign.
Then in December, Belgian authorities arrested 14 men who were allegedly plotting to free an al Qaeda prisoner using guns and explosives.
Now U.S. officials say they are desperately searching to see if the Barcelona cell has ties to any operatives in the United States.
U.S. intelligence has been warning for months that Europe is at risk and could be the gateway to an attack here at home.