Amtrak is holding a high-security exercise Friday in which uniformed officers will be a visible presence on national transit routes. RailSafe will include all the local police agencies along the Amtrak routes involved in the exercise.
"If al Qaeda is planning simultaneous attacks in Europe," said Richard Clarke, former White House national security official and now an ABC News consultant, "there's nothing to say they could not also include the US on that list of simultaneous attacks."
A senior DHS official said the rail exercise is "long-planned" and "is not connected in any way" to the terror threat in Europe.
The stepped-up security comes as the French arrested 12 terror suspects in Bordeaux and Marseilles, and as the U.S. used CIA drones to attack a suspected center of the plot in Pakistan.