Gerard Collomb said that two attackers were arrested in January and one of them had been planning to hit a “major sporting facility”.
The other person, a 33-year-old man, had been targeting soldiers on anti-terrorism patrols.
According to Le Parisien, the second suspect had pledged allegiance to the Islamic State group in a video.
Police had also searched his home in the region of Nimes and found bomb-making equipment.
Mr Collomb told Europe 1 radio: “Because the Islamic State is disappearing, people are seeking to stage attacks in western countries as a distraction from its defeat.
“Terrorism…will still last several years…the threat still exists.”
Neither of the plots were “totally finalise(d)” when a number of suspects were arrested in the cases.
They were known to authorities as having been radicalised and are now in jail, Mr Collomb said.
France prevented 20 attacks last year, according to official figures, but others went ahead: three people were killed on 20 April on the Champs-Elysees in Paris and 1 October at Saint-Charles station in Marseille
Since the attacks against the satirical weekly Charlie Hebdo and the Hyper Cacher store, both in January 2015, terrorists have killed 241 people in France.