Dulles International Airport spokesman Rob Yingling said that some planes were reassigned to other gates for arrival and departure after authorities found a suspicious object on the eve of the 10th anniversary of the September 11 attacks.
Yingling said that the airport was operating normally after the disruption.
The suspicious object was found in a freight container around 4:30pm. Four hours later, it was still being checked by Virginia state police near one of the airport concourses.
Dulles is located about 22 miles west of Washington D.C., where police are on high alert ahead of the 10th anniversary of al Qaeda's attacks on the World Trade Center and Pentagon with hijacked passenger planes. Both cities are again on high alert after receving credible threats about attacks planned for the milestone anniversary.