Police and airport officials say there was nothing harmful about suspicious boxes on a cargo pallet that prompted an hours-long evacuation of several gates at Dulles International Airport.

Metropolitan Washington Airports Authority spokesman Rob Yingling says a detection dog alerted handlers to boxes on a cargo pallet Saturday afternoon. Virginia State Police bomb technicians X-rayed the cargo pallet and a second detection dog sweep determined there was nothing harmful inside. Yingling did not know where the boxes came from or their destination.

Yingling says officials are being extra vigilant in light of recent terror threats, and are taking all precautions.

At least two outbound flights were delayed because the aircraft were within the perimeter, but the closed area was reopened about four hours after the investigation began.