UPDATE, 4:45pm: NBC Dallas-Fort Worth is reporting that a source at the airport told the station that a "suspicious" bag, which housed a printer, was the cause of concern.
PREVIOUSLY: Two men were pulled from American Airlines Flight 1316 in Dallas on Wednesday morning over security concerns, the airline told NBC Dallas-Fort Worth.
After beginning a lengthy security re-screening, the airline opted to cancel the flight, which was bound for Reagan National Airport in Washington, D.C. rather than dispatching it with an excessive delay.
The carrier has not yet said what raised suspicion about the men, though NBC Dallas-Fort Worth reports that a passenger observed what he or she thought was suspicious behavior and then alerted the crew of the single-aisle plane that was scheduled to depart at 10:40 a.m.
American Airlines spokesman Ed Martelle told the Huffington Post that there were "some security concerns aboard the aircraft before it left the gate" and added that "there was one individual who flagged" the suspicious activity.
Martelle also told the Huffington Post that the plane's passengers would be re-routed to Washington on Wednesday, though he could not confirm whether the two men were part of the re-booked group.