It is the first time the red alert level in the Homeland Security warning system has been invoked. Homeland Security defines the red alert as designating a "severe risk of terrorist attacks." One intelligence official said the first-ever red alert signaled extreme concern within the government.

At left, Air Serv employee Shahla Ahmedova confiscated personal items of Dawn Griggs, of Williamsburg, Va., at Dulles International Airport today in Chantilly, Va.