Update 3.25pm: The French Interior Minister has said the man responsible for the attack in Nice had been radicalised very recently.
Later, Interior Minister Bernard Cazeneuve said Bouhlel was not known to the security services, adding: "We are faced with a new type of attack."
And the news channel iTELE said investigators have been told by those under arrest that he recently brought up IS, which he had not done previously, and he had stopped drinking alcohol.
A neighbour of Bouhlel's said he did not believe he was involved with Islamic State.
Speaking outside the high-rise block of flats on Boulevard Henri Sappia, where the suspect had previously lived with his family, Samiq, who did not want to give his surname, said the 31-year-old was not a devout Muslim.
The 19-year-old, who used to play football with Bouhlel, told the Press Association: "I never saw him going to the Mosque. He was not a Muslim. During Ramadan I saw him smoking."
Asked if he thought his neighbour, who he said had moved three years ago but returned often to visit his family, carried out the attack on behalf of the extremist group, he said: "I never heard him speak about extremism, I cannot believe that he was a member of Islamic State."
He said people thought Bouhlel had psychological problems.
"He was a little bit crazy," he said, but the teenager added that he was shocked by what had happened.
Another neighbour, who did not want to be named, said she knew Bouhlel's wife and described her as a "really lovely woman, who doesn't deserve all this".
She added: "She was quiet, she stayed at home with her children. She was a bit naive, she never went out."
The waterfront promenade in Nice was due to re-open at midday on Saturday for the first time since Thursday's attack.
Update 2.30pm: The French President has addressed the nation after the deadly attack in Nice, France.
Update 11.30am: An Irish man believed to have been injured in Thursday's terrorist attack in Nice has been located safe and well.
The Department of Foreign Affairs has said it has no reason to believe an Irish person was caught up in the Nice terrorist attack.
Concerns had been raised about a Galway man believed to have been injured in the Bastille day incident - when a man drove a lorry through a crowd of thousands of people.
However in a statement the Department says there is no longer cause for concern in the case.
Update 10.35 am: The man who drove a truck into a crowd in the French city of Nice is a "soldier" of Islamic State, the group's media outlet said.
The Aamaq news agency cited a "security source" as saying the attacker "carried out the operation in response to calls to target the citizens of coalition countries fighting the Islamic State".
The statement did not name the attacker, and the language implied that he may have acted independently. There is no evidence IS was involved in planning the July 14 attack.
The attack killed 84 people and wounded 200. The driver was identified as Mohamed Bouhlel, a Tunisian known to authorities as a petty criminal.
Earlier:French police have arrested three people in Nice in connection with their investigation into the Bastille day attack that killed at least 84 people.
A lorry ploughed into crowds watching a fireworks display on the seafront on Thursday night.
Authorities are trying to work out if the 31-year-old driver - who was shot dead by police - had any accomplices.
A Galway man is said to be one of 52 people who are in a critical condition following the attack.