According to tracking services, Flight 971 was flying from Rome to Chicago and had just passed Ireland when it turned back and landed at Shannon Airport.
The crew declared a May Day at around 12.45pm and informed air traffic controllers that they wished to divert to Shannon Airport.
"The passengers have disembarked, and the plane and".
A United Airlines flight has been diverted to Shannon this afternoon due to an apparent bomb threat.More news: Ariana Grande and Pete Davidson become engaged
A United Airlines Boeing 737-900ER plane takes off from Los Angeles International airport (LAX) in Los Angeles, California, U.S. March 28, 2018.
United Airlines has confirmed the diversion was due to a "potential security concern".
It's believed that there had been a handwritten note claiming there was a bomb on board discovered in the toilet.
No further details were made available.More news: E3 2018: New Kingdom Hearts III Trailer Features Pirates of the Caribbean
The handwriting on the note was being analysed to see if it matched with any other such notes, which are periodically found on aircraft, one of the sources said.
"We will work to get customers on their way to Chicago as quickly as possible", the statement went on to say.
United Airlines has canceled the final leg of the trip to Chicago and is working to find flights to Chicago for its stranded passengers.
It's understood that no suspicious device was found on-board the plane.. More news: NYCFC hires Man City assistant to replace Vieira
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