Federal authorities have responded to Philadelphia International Airport because of an apparent bomb threat made in connection with an incoming flight from Ireland.
Law enforcement officials met the plane on the tarmac and the 171 passengers and eight crew members exited the jet to waiting buses.
FBI spokeswoman Carrie Adamowski said agents are assisting Transportation Security Administration officials in the investigation.
Police and airport officials said they don't have any specifics about the apparent threat or details about from where it may have originated.
U.S. customs officials have screening facilities at Shannon Airport and the passengers aboard the plane would have gone through them before boarding.