The FBI is examining an explosive device that could have been used by a suicide bomber and which was seized when a plot believed linked to al Qaeda, was thwarted.
The agency says no plane was actually at risk.
US officials say the plot was uncovered at an early stage and no plane tickets had been purchased. There is no indication on the status of the bomber.
The device is a redesigned model of the bomb used by an "underwear bomber" who failed to blow up an airliner bound for Detroit on Christmas Day in 2009. That plot originated in Yemen.
Umar Farouk Abdulmutallab has been sentenced to life in prison for the attempt.
The FBI says it is in possession of the latest device and is conducting technical and forensic analysis on it.
The BBC reports it had a powerful industrial explosive and did not contain any metal.