A man was arrested after threatening to commit an attack while travelling on a high-speed TGV train in eastern France on Friday.
Police sources said the individual threatened to blow up himself or the train. There was no immediate suspicion that terrorism was a motive and the individual's mental health was being investigated, they added.
"This morning, a police officer ... arrested a threatening individual on board a TGV in Moselle. Kudos to him!" Interior Minister Gerald Darmanin said on Twitter.
The officer was off duty at the time, the police sources said. Off-duty policeman are allowed in France to carry a firearm on trains as part of a "travelling to protect" government scheme.
(Reporting by Marine Strauss, Alain Acco; editing by Richard Lough)