ISIS group claimed responsibility for the truck attack in Nice, France. (Reuters Photo)

The Islamic State on Saturday claimed responsibility for an attack that killed 84 in this coastal French city, the organization's news agency said Saturday, as French prosecutors took four more people into custody in connection with the attack.It remained unclear whether the Islamic State had directed the attack, whether they were taking responsibility for an attack that they may have inspired, or whether they were simply seeking publicity from an attack entirely disconnected from them. The Islamic-State-connected Amaq news agency cited an "insider source" saying that Mohamed Lahouaiej Bouhlel, 31, "was a soldier of the Islamic State." The Islamic-State-connected Amaq news agency cited an "insider source" saying that Mohamed Lahouaiej Bouhlel, 31, "was a soldier of the Islamic State.""He executed the operation in response to calls to target citizens of coalition nations that fight the Islamic State," the news agency wrote.But the oblique claim of responsibility left open the question of whether Bouhlel had acted alone or had any prior communication with the group, which has also claimed ties to the attacks that struck Paris twice last year and Brussels in March. French authorities have been scrambling to determine whether Bouhlel acted alone or had a support network in Nice, where he appears to have been living for at least six years.Investigators on Saturday detained three additional people in connection with the attack, including one person who is believed to have spoken to Bouhlel by phone minutes before he started his deadly journey down Nice's Promenade des Anglais, local media reported, adding that an additional man was detained late Friday. Paris prosecutor François Molins said that police had detained Bouhlel's ex-wife and were questioning her.Nice, meanwhile, was trying to return to normal Saturday by reopening the seaside Promenade des Anglais to traffic 36 hours after Bouhlel turned it into a killing field. Beaches were also set to reopen, even as flowers and tributes piled up at a makeshift memorial near the spot where the deadly truck came to a halt. French President François Hollande convened an emergency meeting of his top security advisers to discuss the investigation.The scale of the carnage wrought by a Bouhlel came into grim focus Friday, with 10 children among the dead and 202 people injured. Among the wounded, 50 were "between life and death," according to French President François Hollande.The attack with a 19-ton rented Renault truck - the third mass- casualty assault to hit to France in 18 months - shocked the nation and sparked questions about whether authorities had done enough to safeguard a country that is an obvious target of terrorist groups. Many witnesses said Friday that the packed corniche had been only lightly guarded by police during fireworks on the gently warm night. Bouhlel, a truck driver, was easily able to drive around police fences blocking Nice's famous Promenade des Anglais before jamming on the accelerator and zigzagging his way through the crowds in a method that seemed calculated to generate maximum bloodshed.The identities of the victims testified to France's diverse society and to the international appeal of the tony French Riviera. A vacationing father and his 11-year-old son from Lakeway, Texas. A headscarf-wearing Muslim woman who came to celebrate Bastille Day with her nieces and nephews. A French high school teacher, his wife, daughter and grandson. Others from Russia, Switzerland, Germany, Australia.There were so many victims early Friday that survivors grabbed tablecloths from seaside cafes to cover the bodies strewn across the asphalt. The dead were marked by rectangular orange and white traffic-control barriers that stood like rows of tombstones.Prime Minister Manuel Valls on Friday drew a strong link to terrorism, despite the fact that no militant group had claimed responsibility for the attack and Bouhlel had no known ties to such organizations."The threat of terrorism, as we have now been saying for a long time, is weighing heavily on France, and it will continue to do so for a long time yet," Valls said after an emergency meeting in Paris. "We are facing a war waged on us by terrorism."French citizens are clearly reaching their limit. Valls and Hollande - whose popularity is scraping record lows - were booed when they visited the seaside scene of the attack Friday, in an apparent sign of anger over security lapses.France was shaken by a terrorist attack in January 2015, when militant Islamist attackers took aim at the Charlie Hebdo newspaper and a kosher grocery store in Paris. Attackers struck again in November in a popular nightclub district of the capital, setting off bombs and raking the area with gunfire.This time, the French population had just relaxed after living for weeks on heightened alert during European soccer championships that concluded Sunday. Hours before the violence in Nice, Hollande had announced that he planned to allow a state of emergency to expire at the end of the month. On Friday, Hollande said it would be extended for three months instead, and he said he would boost France's role in the Islamic State strongholds of Syria and Iraq.The attack was a "barbaric act," Hollande said after meeting with top officials in Nice. "An individual who took a truck and murdered people with it."Belgium, Germany and Italy stepped up security along their borders on Friday, in a measure of fears that the violence in France could spill into neighboring countries. Belgium - which was struck by a bomb attack at the Brussels airport and a subway station in March - is particularly nervous ahead of its own national day Thursday.As investigators struggled to understand whether Bouhlel had acted alone, they offered a first account of his path toward the murderous drive that concluded in a hail of bullets from police officers who forced the truck to a stop outside the grand Palais de la Mediterranee, a hotel.Bouhlel was a Tunisian citizen who had lived in Nice since at least 2010, when he first ran afoul of authorities by engaging in petty theft, according to Molins, the prosecutor. Most recently, he had been given a suspended six-month prison sentence related to a January assault, Molins said. In that case, Bouhlel's former attorney told the local Nice-Matin newspaper, a motorist complained the truck driver was blocking the road during a delivery. Bouhlel took a swing at the motorist with a wooden beam, causing a deep wound, according to the lawyer's account. Bouhlel is divorced and has three children, neighbors said. The prosecutor said the suspect's ex-wife was taken in for questioning.As fireworks lit up the sky Thursday in celebration of Bastille Day, Bouhlel drove the rented truck toward its fatal destination, Molins said. In the cab he carried an automatic pistol, two fake assault rifles, a non-working hand grenade and a phony pistol. He swerved around a police barrier blocking the Promenade des Anglais just next to a children's hospital, then sped through the crowds, leaving carnage in his path. More than a mile later, three police officers traded fire with him, Molins said. Authorities think the truck kept going 300 yards after he had been shot. Police found him dead in the passenger seat.Bouhlel was "entirely unknown" to anti-terrorist units, the prosecutor said. "Yesterday's attack has not yet been claimed, but I must stay that this kind of attack is in line with the type advocated by the terrorist organizations in various videos," he said.Witnesses described confusion and chaos Thursday night as hundreds of panicked bystanders ran to try to escape the deadly truck.After the fireworks, Adrien Dobrescu, 54, who was visiting from Romania, heard more sharp bangs. "Someone was screaming, and I saw gunfire," he said. He ran with a crowd as fast as he could off the promenade. "I had waited two, four minutes, I would be dead, too."Survivors were left to deal with the wounded and dead."There were so many injured, and dead bodies," said Fiona Le Goff, 27, a concierge at an apartment building facing the Promenade des Anglais. "The worst was a woman whose body was just stuck to the street."Later, she surveyed the area as forensic teams moved in. "There were people just covered with white cloths," she said. "It was horrible."After the bodies of victims had been hauled away Friday, the macabre truck remained for hours. More than 25 bullet holes riddled its front, and its doors stood open while investigators searched it. Barely 100 yards away, mourners piled flowers and remembrances at the base of a palm tree, some of them crying while they sang "La Marseillaise," France's anthem.© 2016 The Washington Post