Residents of the town of Les Pennes-Mirabeau made the gruesome discovery when they investigated an explosion in a pine grove shortly before midnight.
Pennes-Mirabeau lies just 14 kilometres north of the southern port city of Marseille.
TV channel LCI reported on Sunday evening that the bodies had been shot.
Last week, the charred body of a resident of Marseille was found in a burning car in a parking lot in Septemes-les-Vallons, a town close to Les Pennes-Mirabeau.
The man, who had a criminal record for drug trafficking, had been shot in the head.
The region has seen several similar executions in recent years.