French anti-terror police were holding two suspects Wednesday after finding several gas cylinders in a car near Paris's Notre Dame cathedral, sources close to the investigation said.

No detonators were found in the vehicle, which was discovered abandoned at the weekend, the sources said.

The car's owner and an associate, both known to police, were arrested on Tuesday, they said, adding a preliminary investigation had been launched.

Notre Dame, a Gothic cathedral famous for its flying buttresses, stained glass windows and gargoyles, is one of Paris's key landmarks, attracting 13 million visitors each year.

A bar employee working nearby raised the alert on Sunday after noticing a gas cylinder on the backseat of the car, whose hazard lights were flashing and which had no number plates, a police source said.

The car was parked in a side street opposite the cathedral on the left bank of the Seine, the police source said, adding that the car's owner was identified on Tuesday.

France has been rocked by a string of deadly attacks claimed by Islamic State (IS) group militants.

In July, 86 people were killed when a truck ploughed into a Bastille Day crowd in the southern resort of Nice with IS saying it was driven by one of its followers.

Less than two weeks later, two young jihadists murdered a priest near the northern city of Rouen.

IS also claimed responsibility for the November 2015 attacks on Paris that killed 130 people and injured hundreds.

The head of France's DGSI domestic intelligence service, Patrick Calvar, warned in May of a ‘new form of attack’ in which explosive devices would be left near sites that attract large crowds.