Explosives, 180 detonators and around 40 grenades were stolen from an army base in the southern French town of Miramas, near Marseille, a source close to investigation said on Tuesday.
The theft came even though France has heightened security after a suspected Islamist beheaded his boss and tried to blow up a gas plant near Lyon on June 26. Six months earlier, gunmen killed 17 people at the offices of satirical weekly Charlie Hebdo and a Jewish foodstore in January.
The Marseille prosecution office has begun an investigation into the robbery, which was discovered on Monday. France's defence ministry ordered a review of the army's military supplies and the protection of ammunition storage units.
The Miramas site serves as a logistical base for the French army's external operations, the source said.