A United Airlines flight traveling from Rome to Chicago was diverted to Ireland due to a "potential security concern," the airlines said in a statement. United flight 971, a Boeing 767-300, landed in Shannon, Ireland, on Monday, and Irish police are interviewing passengers and crew members.
A source familiar with the matter said a written bomb threat was found onboard the aircraft, which was carrying 107 passengers, eight flight attendants and three pilots.
The Irish Times reports that the threatening message was scribbled on a surface inside one of the plane's bathrooms.
The aircraft will be swept for explosives and passengers will be subject to additional security screenings. United expects passengers will need to stay the night in Ireland and return to Chicago on Monday as police continue their investigation.
"We will work to get customers on their way to Chicago as quickly as possible," the company said.
CBS News' Kris Van Cleave contributed to this report.