Nice 'has been jihadist breeding ground for years'
Dozens of people have travelled from Nice to join Islamic State, an expert said.
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."
Focus has turned to a message from an IS spokesman nearly two years ago which listed running over victims with a car as a possible means for carrying out attacks.
There has been no formal claim of responsibility from any organisation so far.
Another expert said intelligence agencies in France and around Europe will be working to establish whether the attacker was acting alone or linked to or inspired by any organisation.
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?"