In one of the worst terror attacks France has witnessed recently, a lorry ploughed through packed crowds in Nice, Southern France, leaving 80 dead bodies in its wake and another 100 critically injured. The investigation "will try to determine whether he benefited from accomplices [and] will also try to find out whether Mohamed Laouaiej Bouhlel had ties to Islamist terrorist organizations".
French Prime Minister Manuel Valls told the evening news that Bouhlel was "one way or another" linked to radical Islam.
Mr Hollande, who says the attack was a terrorist act, has already extended a state of emergency by three months.
The new advice said: "If you're in the area, follow the instructions of the French authorities, who have cancelled a number of public events planned for the coming days, closed the Promenade des Anglais and a number of the public beaches in and around Nice, and implemented some traffic restrictions".
Wassim Bouhlel, a native of Nice, told The Associated Press he saw a truck drive into the crowd, then its driver emerged with a gun and started shooting.
No group claimed responsibility for the slaughter of tourists and locals packing the upscale seafront, where an estimated 30,000 had just watched a Bastille Day fireworks show.
Bouhlel was shot and killed by police.
"This is making Europe so much weaker at a time when Europe doesn't know what it stands for", said Ian Bremmer, head of consulting firm Eurasia Group. They had come to marvel at the fireworks, "to feel joy, to share in happiness and be dazzled", said President Francois Hollande.
It's been the case for the previous year or two, if not a little bit more than that.
Tour de France observes moment of silence..
French President François Hollande has declared three days of mourning and extended the state of emergency that has been in place since the country's last attacks on November 13, 2015, which killed 130 people around Paris.
President Obama Calls Attack On Nice 'Appalling,' 'Sickening'
The United Nations Security Council said it "condemned in the strongest terms the barbaric and cowardly terrorist attack".
His father said he had suffered from depression and had "no links" to religion. El Shafei said he saw the driver, later identified by authorities as Mohamed Bouhlel, fire back through a window.
Neighbours described the attacker, who was born in Sousse in Tunisia and lived in a modest district of Nice, as a loner who never responded to their greetings. He had three children.
Some witnesses suggested that the police were lulled into a sense of security after the soccer tournament took place without incident.
The truck's windshield was left riddled with bullet holes. Inside the truck, police found a large cache of firearms and grenades.
Pediatric surgeon Frederico Solla told reporters outside the children's hospital that his team had been prepared for an attack and had even run simulations in the lead up to Euro 2016, but that nothing could prepare them for the dozens of children with horrific injuries that arrived Thursday night. Some were "hanging between life and death".
Cazeneuve said "we are in a war with terrorists who want to strike us at any price and in a very violent way".
"You would think you could do something to help by being there", said Tarubi Wahid Mosta, who tried to do what he could in the aftermath of the attack. "It looked like a battlefield", Mosta said.
Obama made the comments during a White House reception Friday for diplomats from around the world.
The president also spoke of recent attacks in Turkey, Iraq, Bangladesh and Saudi Arabia, mostly nations that belong to an worldwide coalition fighting the Islamic State: "We can not give in", he said.
"Tragic paradox that the subject of Nice attack was the people celebrating liberty, equality and fraternity", European Council President Donald Tusk said on Twitter.