TORONTO (AP) — Passengers on a flight set to travel from Toronto to Chicago have experienced lengthy delays after what U.S. authorities describe as a security breach aboard the plane.

U.S. Customs and Border Protection says officials found what they describe as a mock improvised explosive device inside a passenger's suitcase at Pearson International Airport, Canada's busiest.

The agency says the passenger was scheduled to travel on United Airlines flight 547.

All passengers and luggage were removed from the plane.

Peel Regional Police in Ontario province say they are now responsible for the investigation. But they have not released details or indicated whether any charges are pending.

Passengers on the flight complained of long delays Thursday and said the plane sat on the tarmac for four hours.