French prosecutors say the men are Tunisian and French
Eight new arrests have been made over the Bastille Day lorry attack in Nice that left 86 people dead.
Prosecutors said the suspects, who are French and Tunisian, had links to the attacker, Mohamed Lahouaiej Bouhlel.
They were detained on Monday in the Alpes-Maritimes region, which includes Nice.
At least five others already face preliminary terrorism charges - accused of helping Bouhlel to get a pistol and of providing other forms of support.
Bouhlel, who was shot dead by police, was a Tunisian with French residency.
He drove a truck through a crowd that had assembled for a fireworks display on Nice's Promenade des Anglais, killing 86 people and injuring a further 434.
Islamic State has claimed responsibility for the attack on July 14th.
But while the French authorities said Bouhlel had been inspired by IS's propaganda, they said they had not found anything to show that the group actually orchestrated the assault.
Bouhlel had driven more than a mile in the rented truck, zig-zagging across the road to mow down as many people as possible, witnesses said.
Many people fled into the sea to escape the attack, with witnesses telling how people were "flying like bowling pins" as Bouhlel went on the rampage.
Bouhlel also shot three police officers before he was killed.
His father, Monthir Bouhlel, said his son had undergone psychiatric treatment in the past and was unstable and sometimes violent.