(CNN) The man who used a 20-ton truck to plow down hundreds of people in Nice this week, killing 84, somehow became rapidly radicalized and hadn't shown up on any anti-terrorist intelligence radar, French Interior Minister Bernard Cazeneuve said Saturday.

The minister said Mohamed Lahouaiej Bouhlel, 31, had had no record of making militant statements and was not known to the intelligence services.

It seems he became radicalized very quickly," Cazeneuve said, without offering specifics.

"This is a new type of attack," Cazeneuve said. "We are now confronted with individuals that are sensitive to the message of ISIS and are committed to extremely violent actions without necessarily being trained by them."

Earlier Saturday, a statement from ISIS' media group, Amaq Agency, said that an ISIS "soldier" carried out the attack in Nice.

People left flowers, candles and other tributes in Nice, France, on Saturday in memory of those killed in Thursday's terror attack in the coastal city.

The statement, which was posted by ISIS supporters, said a security source told the agency "the person who carried out the run-over in Nice, France, is one of the Islamic State soldiers and carried out the operation in response to calls to target nationals of the coalition which is fighting the Islamic State."

Mohamed Lahouaiej Bouhlel's ID Card

The wording of the statement -- not claiming the attack as an outright act of ISIS, but noting that the attacker was responding to calls to act against the coalition -- mirrors ISIS' language in statements after the nightclub shooting in Orlando, when it claimed gunman Omar Mateen as a "soldier." Forty-nine people died in the June 12 massacre.

French prosecutor François Molins said Friday the attack in Nice fits with calls that "terrorist organizations regularly give out on their videos and elsewhere."

New developments in the investigation

As the investigation continued, French authorities were questioning five people Saturday. Among them was Bouhlel's ex-wife, who was taken into custody Friday, the anti-terrorism prosecutor's office said. The other four are men.

Bouhlel, a resident of Nice, was born in Tunisia but had a permit to live and work in France.

While Cazeneuve said no evidence had yet been found to tie Bouhlel to jihadism, a source close to the investigation told CNN that a phone number belonging to Bouhlel cropped up in a counterterrorism investigation into an associate of Omar Diaby, a 41-year-old Senegalese jihadi who lived in Nice before traveling to Syria.

Diaby, who calls himself Omar Omsen, commands a French jihadi battalion in Syria affiliated with Jabhat al Nusra, al Qaeda's branch in Syria. The source said investigators made the link after cross-referencing case files after the attack in Nice. Investigators are looking into the nature of the links between Bouhlel and Diaby's associate, but they cannot rule out that the two were possibly just part of the same social circle.

French counterterrorism officials have established that a series of YouTube videos Diaby recorded in Nice in 2012 before he departed for Syria helped motivate a significant number of French extremists to travel to fight in Syria. In May, Diaby revealed in a Skype interview with a French journalist that he had faked his own death in August 2015 to get medical treatment outside Syria.

Hollande warns of continued strikes

French President François Hollande, addressing his country after its third major terrorist attack in 18 months , described the assault as an "unspeakable act."

"We have an enemy who is going to continue to strike all the people, all the countries who have freedom as a fundamental value," Hollande said.

Photos: Bastille Day terror: Harrowing images of truck attack in Nice Photos: Bastille Day terror: Harrowing images of truck attack in Nice Baby strollers are seen on the Promenade des Anglais in Nice, France, on Friday, July 15. A 31-year-old native of Tunisia and resident of Nice drove into a crowd during the southern French city's Bastille Day celebrations around 10:45 p.m. on Thursday, July 14, killing at least 84 people and leaving around 202 injured. Hide Caption 1 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice A woman cries, asking for her son, as she walks near the scene of the attack. Hide Caption 2 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice A forensics team inspects the scene of the attack. Hide Caption 3 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice A man looks at the scene of the attack on the Promenade des Anglais. Hide Caption 4 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice Forensics investigators examine a truck at the scene of the attack. Hide Caption 5 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice Hide Caption 6 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice Bodies of victims covered by sheets remained at the scene of the attack early Friday. Hide Caption 7 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice A man sits next to the body of a victim following the attack. Hide Caption 8 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice Authorities confirmed that the driver of the truck was killed by police. Hide Caption 9 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice The truck plowed into a crowd leaving a Bastille Day fireworks display in the French resort city of Nice. One witness, an American who was about 15 feet from the truck, said the driver accelerated and pointed his tractor-trailer into the crowd, mowing people over. Hide Caption 10 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice A man lies near a covered body at the scene of the attack on the Promenade des Anglais in Nice. Hide Caption 11 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice Emergency teams assist wounded people at the scene. Hide Caption 12 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice A photo from the Twitter account of a reporter for CNN affiliate France 2 shows witnesses being interviewed inside the Hotel Negresco after the attack. According to Alban Mikoczy, these people are not injured. Hide Caption 13 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice Wounded people are evacuated from the scene where the truck drove into the crowd during the Bastille Day celebrations. Hide Caption 14 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice Armed French police move people away from the Promenade des Anglais in Nice in the aftermath of Thursday's attack. Hide Caption 15 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice Medical workers attend to an injured woman. Hide Caption 16 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice Police security forces deployed in the center of Nice. Hide Caption 17 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice Tony Molina, a U.S. police officer on vacation in Nice, witnessed the terrible scene from his hotel room. He told CNN he thought he heard between 30 and 40 gunshots. "I saw the truck right below us and it had already driven down the boardwalk for a half a mile." Hide Caption 18 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice BFM-TV, a CNN affiliate in France, reported that police shot at the truck to try to stop it. Hide Caption 19 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice Rescue workers move a victim from the scene. Hide Caption 20 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice Soldiers, police officers and firefighters walk among bodies covered with blue sheets on the seafront Promenade des Anglais. Hide Caption 21 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice Police seal off the area around the scene. A witness said at first it seemed like an accident, but then it became obvious it was a deliberate act. Hide Caption 22 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice "I wasn't sure what to do, in that situation. No one knew what was going on. We just knew we had to run for our lives," said Paul Delane, an American who witnessed the attack. Hide Caption 23 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice French President François Hollande said the country would now extend its state of emergency for three months. Hide Caption 24 of 25 Photos: Bastille Day terror: Harrowing images of truck attack in Nice A doll is seen at the scene of the attack on the Promenade des Anglais. Hide Caption 25 of 25

Bouhlel was shot to death by police after he barreled down the crowded Promenade des Anglais for almost a mile, crushing and hitting people who had gathered to watch the Bastille Day fireworks. More than 200 people were injured, and at least 55 of them were in critical condition Friday.

Bouhlel was identified by fingerprints after his identification card was found in the truck, authorities said.

He was known to police because of allegations of threats, violence and thefts over the past six years, and he was given a suspended six-month prison sentence this year after being convicted of violence with a weapon, authorities said.

Bouhlel's father, who lives in Tunisia, said his son showed signs of mental health issues -- having had multiple nervous breakdowns and volatile behavior, said CNN terrorism analyst Paul Cruickshank.

Despite his criminal record, Bouhlel was not on the radar for any kind of terror threat. The man was "entirely unknown by the intelligence services, whether nationally or locally," Molins said.

"He had never been the subject of any kind of file or indication of radicalization."

'There are dead everywhere'

As the seaside resort town tried to regain a semblance of normalcy Saturday, harrowing new details emerged about Thursday night's tragedy. One young victim, Kimberley Torres, described how someone tried to throw her out of the way of the truck, but she was still hit by it.

"I tried to roll myself into a ball, so the people wouldn't crush me, but I was still hit in the stomach and leg," she said.

The 16-year-old, who lives in Nice and is studying for an international baccalaureate, is recovering from her injuries at the Fondation Lenval.

On a normal day, the stunning beach here in #Nice would've been packed. Instead, it's closed as #France mourns again pic.twitter.com/rjFswa9yT5 — Will Ripley (@willripleyCNN) July 15, 2016

Her mother, Edvige Torres, said she would take her daughter to a psychologist when her physical wounds had healed. She said her daughter called her in tears because she had been separated from her best friend, whom Kimberley was later reunited with and who was unharmed.

"The most awful thing for her, amidst all this is ... she was telling me: 'Mum, there are dead everywhere, severed heads, severed people, there's blood everywhere, mother, come.'"

Edvige Torres said she immediately left her home near the beachfront to find her daughter, whom she then took straight to a hospital.

"I've tried to keep my head until now, but I can't anymore," she said.

'Bodies flying in the air'

Another student said he saw the attack from the balcony of his friends' flat.

Andres Farfan, a 21-year-old from Peru, was celebrating finishing his university degree in Nice when he heard screams coming from the beachfront.

He looked down and saw the truck speeding on the footpath of the road.

Wounded victims of the attack in Nice, France, are evacuated from the scene.

"It was going pretty fast, I guess 60 or 70 kph, and people were screaming and trying to avoid it, and some jumped to the beach side, and it is not small sized, it's a big jump," Faran said.

Most people on the boulevard struggled to avoid the truck as it approached.

"At that point I thought that these people wouldn't make it, because it was really fast and they were all together like a pack," he said. "I couldn't watch it. I closed my eyes, and I went inside the apartment. Some of my friends did the opposite -- they went outside, when people started screaming, they went and saw this; then they started screaming and crying immediately. I can't imagine what they have seen.

"They say they saw bodies flying in the air when the truck hit them."

Farfan braced himself to go out on the balcony to see the aftermath. "We saw the first scenes of the bodies, the uncovered bodies, the dead. I saw a bunch of six, seven bodies -- they were stuck to the floor with blood around them. It was horrible to watch."

Before the attack

Bouhlel began the attack about 10:45 p.m., authorities said. At one point, he fired a gun several times at three police officers close to a hotel, the prosecutor said.

The truck he used was rented on Monday and was supposed to have been returned Wednesday, Molins said, without specifying who rented it. Surveillance video shows that about two hours before the attack Thursday, Bouhlel rode a bicycle to pick up the truck east of the city, the prosecutor said.

After Bouhlel was shot, police found a handgun and some ammunition in the truck's cab, as well as a replica handgun, two replica assault rifles, a cell phone and various documents, Molins said. In the trailer was the bicycle and some empty pallets.

Hollande declared a national mourning period from Saturday to Monday.

France was just preparing to lift its state of emergency, which was put into place in the wake of the November terror attacks in Paris that killed 130 people, the deadliest attack in France's history.

Nice is just the latest city to be hit by a terror attack. Istanbul, Orlando, Baghdad, Brussels and Dhaka in Bangladesh are among other targets hit in recent months.

'Big step back'

Cruickshank said "no country in the Western world is threatened more by jihadis and terrorism than France."

"This is a big step back here. They are absolutely exhausted after a year and a half of intense efforts to try and protect this country," Cruickshank said.

"The painful reality here is that if it wasn't going to be this promenade, it would have been any other promenade."