Homemade explosives ready for use have been found in an unoccupied flat near Paris, French judicial sources said.
Gas canisters and electric wiring were also found in the flat in Villejuif, a suburb south of the French capital, and two men were arrested nearby, the sources said.
The explosive, known by the initials of TATP, is notoriously used by the so-called Islamic State group, which has repeatedly targeted France in recent years.
Police also found ingredients that can be used to produce TATP as well as papers written in Arabic.
Anti-terror prosecutors have opened an investigation, sources close to the probe said.
One of the two arrested men, aged 36 and 47, is the owner of the flat, they said.
Paris police said a man who works at the apartment block had alerted police to "suspect items" in the apartment.
Interior Minister Gerard Collomb praised the individual for his "citizen's reflex".
A jihadist cell behind twin attacks that claimed 16 lives in Barcelona and Cambrils, Spain, last month had been preparing TATP.
Investigators probing a house that been wrecked by an explosion found acetone and other TATP ingredients, as well as 120 butane canisters and detonators.
The car used by the assailants in Cambrils had been in the Paris area less than a week before the attacks.
But a source close to the probe sparked today said: "At this stage there is nothing to link the discovery of these items (in Villejuif) to the Catalonia cell."
France has been under a state of emergency since IS jihadists struck in Paris in November 2015, leaving 130 people dead.
Since that large-scale attack and last year's Nice truck attack that killed 86, France has suffered a string of smaller assaults mainly targeting security forces.