NICE, France (AP) – The mayor of Nice called Monday for France to step up its fight against extremism, saying the attack on his city shows that radical ideas are still entering the country too easily.

Speaking four days after a man drove a truck through Bastille Day crowds, leaving at least 84 people dead and hundreds more injured, Mayor Philippe Pradal warned that France has some way to go in preventing extremists from launching similar attacks on its territory.

“I think we haven’t necessarily learned all of the lessons from the fact that our country is at war,” Pradal told The Associated Press in an interview.

French authorities say they believe Mohamed Lahouaiej Behloul became radicalized shortly before the attack, having previously shown little tendency toward religious extremism. The Tunisian-born Behloul had a rap sheet for petty crime, consumed alcohol and chased after women according to people who knew him. Yet within 48 hours of the attack, the Islamic State group claimed him as one of its foot soldiers, suggesting that volatile people such as Behloul may be prone to rapid radicalization, thereby posing a hard to calculate risk for authorities.

Pradal, the mayor, noted that responsibility for security during the July 14 fireworks display lay primarily with the national authorities and that anti-terrorism procedures were followed. Whether those were sufficient is part of the investigation now being conducted, he said.

Additional security measures might have reduced the death toll that was caused partly by the speed with which Behloul drove his rented truck onto the seafront promenade and then through crowds of surprised revelers, including many children.

“Greater security infrastructure would probably have slowed down the progress of the truck, but we don’t have certainty that it would have stopped it,” said Pradal. “Experience will unfortunately teach us to plan better and establish a more efficient security infrastructure that stops this type of behavior, but in this case what was set up by the national police didn’t stop the truck from taking its tragic course on the Promenade des Anglais.”

Pradal said the attack in Nice, which follows two mass killings by Islamic extremists in Paris last year, shows that his city represents a particular target for extremists because of its long history as a Mediterranean melting pot that is tolerant of all nationalities and religions.

In recent years Nice has also seen a disproportionate number of young Muslims joining jihadist groups fighting in Syria and Iraq, prompting local authorities to put in place a range of measures intended to spot radicalization and encourage friends or family members to report what Pradal called “weak signals” such as changed eating habits or sudden interest in religion.

Those measures failed to stop Behloul, who appears to have methodically planned the attack that ended only when he was shot dead by police.

Investigators are now scouring the 31-year-old’s phone messages and online activity, looking for possible accomplices and signs that might have pointed to his radicalization.

Pradal said that for many extremists the process of radicalization takes place on the Web, requiring greater surveillance effort by the state.

“We are at war and we will not win the war with the tools of peace,” he said, suggesting that the fight needs to be taken to IS, including in the virtual realm.

“The intelligence services need to be increasingly aware of the information that is being spread online because it’s a tool of war almost as important as weapons,” he said.