French police have reportedly detained eight men linked to lorry attacker Mohamed Lahouaiej Bouhlel, who murdered 86 people on the seafront at Nice.
Police carried out a wave of arrests on Monday and Tuesday in and around Nice.
Bouhlel drove a lorry into a crowd celebrating Bastille Day on 14 July.
He was originally thought to have acted on his own, but prosecutors later said he had accomplices. Six suspects have already been placed under formal investigation as part of the inquiry.
The attack was claimed by jihadist group Islamic State (IS), and anti-terror prosecutor Francois Molins said it had been planned for months in advance.
The six initial suspects have been accused of providing Bouhlel either with a pistol or with logistical support.
The latest arrests involve French and Tunisian men, reports say.
Ceremonies were held on Monday to remember the 229 victims of jihadist attacks in France since the start of 2015.
Yasmine Bouzegan Marzouk, who lost three members of her family in the Nice attack, gave a passionate speech in Paris in which she said "these barbarians have no law, no faith, no religion".
A Muslim herself, Ms Marzouk told how her 13-year-old relative Mehdi Hachadi was killed under the wheels of Bouhlel's lorry.
"The life of a child who had such a promising future was snatched away. He was brought up in the Muslim faith, which says we should respect others and show tolerance," she said.
Bouhlel himself was eventually shot dead when police surrounded his 19-tonne lorry.