A second couple was detained overnight in connection with an investigation into the discovery of a car in Paris containing six gas cannisters, a French police source said Thursday.
The pair was picked up near Montargis, about 110 kilometres (65 miles) south of Paris.
Their detention raises to four the number of people held in connection with the suspect car, an abandoned Peugeot 607 which was parked several hundred metres from Notre Dame cathedral in Paris.
The first couple, who were detained at a service station on a road in southern France, were known to the security services for having links to radical Islamists.
The daughter of the car's owner, described by her father as being radicalised, is also wanted for questioning, police said.
Anti-terror investigators are probing the incident which comes as France is on high alert following a string of terrorists attacks.