A transatlantic flight was last night diverted to Shannon Airport after a note - understood to include a bomb threat - was found in a toilet on board.
United Airlines said flight UA971, from Rome to Chicago, was diverted due to a "potential security concern".
The message is reported to have referred to a bomb on the plane.
Gardaí were taking handwriting samples from the 207 passengers to establish if one had written the message.
In a statement, United Airlines said: "After assessing the situation our crew made the decision to divert to the nearest available airport.
"Additional security screenings will be performed on all customers and baggage, and we will work to get customers on their way to Chicago as quickly as possible."