The office said the suspects detained Monday were French and Tunisian and had links to the attacker, Mohamed Lahouaiej Bouhlel, who plowed a 19-ton truck down Nice's Promenade des Anglais and into a crowd assembled for a July 14 fireworks display.
All eight were arrested in the Alpes-Maritimes region in the southeastern corner of France that includes Nice.
At least five people already face preliminary terrorism charges in the attack, and are accused of helping Bouhlel obtain a pistol and providing other support. It was not immediately clear what role is suspected for the men arrested this week.