A week after Mohamed Lahouaiej Bouhlel ploughed a 19-tonne truck into a crowd, killing 84 people, five suspects arrested over links to the Tunisian were to appear before anti-terrorism judges who will decide whether to charge them.
Lawmakers also adopted a law extending a state of emergency for six months, after it was toughened up by the right-dominated Senate.
The final version bans gatherings where sufficient security can not be provided and makes it easier to shut places of worship where preachers incite hate or violence.
Interior Minister Bernard Cazeneuve called for a police inquiry into the security measures taken in Nice, after an article in Liberation daily claiming that only one municipal police car was guarding the spot where Bouhlel crashed through barriers onto the promenade.
Also Read
Cazeneuve has criticised the article as false and Prime Minister Manuel Valls has accused opponents who suggest the Nice attack could have been thwarted of "lying to the French".
The latest attack, which was claimed by the Islamic State group, has politicians tearing into each other, a far cry from the display of unity 18 months ago after the first strike against the Charlie Hebdo magazine and a Jewish supermarket.
However while IS claimed Bouhlel was one of its "soldiers", it has yet to publish footage or photos of the Tunisian as it did after previous attacks.
Investigators have said they have no proof yet that the driver, who was shot dead by police, had pledged allegiance to the group.
In Nice, investigators found a Kalashnikov rifle and a bag of ammunition in the basement of a 22-year-old man who is among five being held over links to Bouhlel.
All five suspects -- four men and a woman -- are to appear before a judge to face possible charges.
About 100 investigators are poring over masses of data linked to the probe.
Pictures found on Bouhlel's cellphone indicate he was studying several locations where crowds gathered as possible targets.