The driver of the lorry in the Nice attack has been identified as a 31-year-old French-Tunisian.
Unconfirmed reports named the man as Mohamed Lahouaiej Bouhlel. He was said to be known to authorities in connection with anti-social behaviour, but not to French intelligence services.
The moment the attacker was shot dead by police was captured on film by a witness. Some viewers may find the footage disturbing.
Police investigating the atrocity have raided a property in Nice, according to local media.
The Nice Matin newspaper also reported that family members were speaking to the police, and officers were conducting operations in the city to find any possible accomplices.
ID papers were believed to have been found in the truck - said to have been hired in a neighbouring town on Wednesday.
Scores of people including several children died after the vehicle drove through crowds celebrating Bastille Day in the city in the south of France.
Eyewitnesses said the driver swerved from side to side as he drove for hundreds of metres along the famous Promenade des Anglais on the seafront, before he was shot dead by police.
Margaret Gilmore, senior associate fellow at security think tank the Royal United Services Institute, said: "There has been no claim of responsibility yet, but certainly the working theory is that this is a terrorist attack.
"This individual may well have either been inspired by or had links to Isis, but we do not know for sure."
She added: "The intelligence agencies will be trying to work out if he was working alone.
"The British will be doing exactly the same thing, they will be putting his name into their data systems here - was he a member of Isis, did he have friends in Isis, or was he simply inspired by them or some other group?"
Peter Neumann, director of the International Centre for the Study of Radicalisation and Political Violence at King's College London, described the area as a "jihadist breeding ground".
He said: "Securing the borders would have been some kind of solution in relation to the Paris attacks, where the attackers came from Belgium, but we will have to see in this particular case whether the attackers are from outside or actually from Nice.
"Because Nice, for anyone who has been following this, has been a jihadist breeding ground for a number of years.
"We've seen dozens of people going from Nice to the Islamic State, to Syria, and the first recorded attempted attack in Europe was very nearby in Cannes, so it's likely the attackers are from within the vicinity, rather than abroad."
He added: "If it turns out this was not a so-called lone wolf attack but directed from within Syria and Iraq, then it would make sense to try to eliminate the sanctuary, the safe haven that IS enjoys in Syria and Iraq, but at this stage we just don't know.
"What many people have speculated is that as Iraq and Syria become less of a state for IS, they are resorting to more terrorism abroad, almost trying to compensate for their losses, by lashing out in Europe and elsewhere. In that sense, fighting them in Iraq and Syria may have the opposite effect."