Paris - Two suspects were in custody on Wednesday after French police found several gas cylinders in a car near Paris's Notre Dame cathedral, sources close to the investigation said.
Anti-terror prosecutors have opened a preliminary investigation, the sources said, adding that no detonators were found in the car.
The car's owner and an associate, both known to police, were arrested on Tuesday, they said.
Notre Dame is one of Paris's most visited landmarks attracting 13 million visitors each year.
France has been rocked by a string of deadly attacks claimed by Islamic State 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.
