A car, whose owner is on an intelligence services watchlist of people suspected of religious radicalization, was discovered near Notre-Dame cathedral in Paris on Saturday, September 3 night with seven gas cylinders inside, police and judicial officials said on Wednesday, according to Reuters.

The car owner was taken into custody but later released, one judicial official said. A couple, aged 34 and 29, were arrested at a motorway lay-by on Tuesday in southern France in connection with the incident and remained in custody, the official said.

The Peugeot 607, which had no registration plates, contained seven gas cylinders, one of them empty on the front passenger seat, two police officials said.

It was found with its hazard lights flashing, as if to attract attention, they said.

Interior Minister Bernard Cazeneuve said he was waiting for a report from investigators on what the possible motives were for the incident.

There was no detonating device present in the car, found on a Seine riverside stretch called the Quai de Montebello, meters from the Notre-Dame cathedral, one of Paris's many popular tourist attractions.

Documents with writing in Arabic were also found in the car.

More than 200 people have been killed in terror attacks over the past year-and-a-half in France. France remains on maximum alert after calls by the Islamic State group for followers to attack the country, which is bombing the militant group's bases in Iraq and Syria.