Authorities have yet to produce evidence that Mohamed Lahouaiej Bouhlel, 31, shot dead by police, had links to Islamic State, (IS) which claimed the attack, but Mr Valls said there was no doubt on the assailant’s motives.
“The investigation will establish the facts, but we know now that the killer was radicalised very quickly,” he said in an interview with Le Journal du Dimanche. “The claim on Saturday morning by Islamic State and the fast radicalisation of the killer confirms the Islamist nature of this attack.”
Officials said people questioned by police had indicated that he had undergone a rapid transformation from someone with no apparent interest in religion. Relative and friends interviewed in Nice painted a picture of a man who at least until recently drank alcohol, smoked marijuana and, according to French media, even ate pork, behaviour that would be unlikely in a devout Muslim.
Speaking from his home town in Tunisia, Bouhlel’s sister said he had been having psychological problems when he left for France in 2005 and had sought medical treatment. As authorities were trying to better understand his motives, two more people, a man and a woman close to Bouhlel, were arrested in Nice early yesterday, bringing the number of people in detention to seven.
The Amaq news agency affiliated with the militant Islamist group said Bouhlel “was one of the soldiers of Islamic State”.
Mr Valls, who said security services had prevented 16 attacks over three years, indicated that Thursday demonstrated the group’s modus operandi of cajoling unstable individuals into carrying out attacks with whatever means possible.
“Daesh gives unstable individuals an ideological kit that allows them to make sense of their acts... this is probably what happened in Nice’s case,” Mr Valls said, using the Arabic acronym for IS.
The group, under military pressure from forces opposed to it, considers France its main target, given its operations in the Middle East, and also because it is easier to strike than the US, which is leading a coalition against it.
Despite mounting criticism from the conservative opposition and far-right over how president Francois Hollande’s Socialist government is handling security, Mr Valls said there was no risk zero and new attacks would occur.
“I’ve always said the truth regarding terrorism: There is an ongoing war, there will be more attacks,” he said. “It’s difficult to say, but other lives will be lost.”
With presidential and parliamentary elections less than a year away, French opposition politicians are increasing pressure and seizing on what they described as security failings that made it possible for the truck to ram 2km through large crowds before it was finally halted. After Thursday’s attack, a state of emergency imposed across France after the November attacks in Paris was extended by three months and military and police reservists were to be called up.
A former neighbour of Bouhlel said the 31-year-old had never spoken about extremism.
Speaking outside the high-rise block of flats on Boulevard Henri Sappia, where the suspect had previously lived with his family, Samiq, 19, who did not want to give his surname, 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,” Samiq said, but he added that he was shocked by what had happened.
The apartment on Route de Turin where Bouhlel was believed to be living before the attack was raided by police, and a view through the keyhole showed items including what appeared to be boxes of medication and a strip of tablets. The driver’s father has said that Bouhlel had received psychiatric treatment in the past.
He told French television that the family had sought medical treatment after his son had a breakdown.
“He had psychological problems that caused a nervous breakdown; he would become angry, shout, break everything around him.”