Tourists and citizens stand by flowers laid near the scene of a truck attack in Nice, southern France, Saturday, July 16, 2016. Nice's seaside boulevard reopens to traffic Saturday following a dramatic truck attack which killed more than 80 people and wounded more than 200 others at a fireworks display. (AP Photo/Luca Bruno)
Tourists and citizens stand by flowers laid near the scene of a truck attack in Nice, southern France, Saturday, July 16, 2016. Nice's seaside boulevard reopens to traffic Saturday following a dramatic truck attack which killed more than 80 people and wounded more than 200 others at a fireworks display. (AP Photo/Luca Bruno) Credit: Luca Bruno

Seeking to quell fear and criticism, the French government called up thousands of police reserves Saturday to increase security around the country, after the Islamic State group claimed responsibility for a beachfront Bastille Day attack that security forces failed to thwart.

Critics lashed out Saturday at President Francois Hollandeโ€™s Socialist government, asking how a country still under a state of emergency after previous carnage from Islamic extremist attacks could have let this happen again.

Hollande held an emergency security meeting Saturday, and late in the day Interior Minister Bernard Cazeneuve announced he would call up 12,000 police reserves in addition to more than 120,000 police and soldiers already deployed around the country โ€œbecause of the terrorist threat.โ€

The investigation focused on attacker Mohamed Lahouaiej Bouhlel, a 31-year-old Tunisian who had lived in Nice for several years, and whether he acted alone while driving a truck through the holiday crowd. He was shot dead by police Thursday night โ€“ and witnesses who saw him said he appeared determined to kill as many people as possible.

ISIS said Saturday that the attacker was one of its โ€œsoldiers,โ€ the first claim of responsibility. It didnโ€™t name Bouhlel, but the statement, quoting an ISIS security member, said he was following ISIS calls to target citizens of the countries fighting the extremists.

The veracity of the groupโ€™s claim couldnโ€™t immediately be determined, but French officials didnโ€™t dispute it.

What is known publicly about Bouhlel so far suggests a troubled, angry, sometimes violent man with little interest in the groupโ€™s ultra-puritanical brand of Islam. Neighbors described the father of three as a volatile man, prone to drinking and womanizing, who was in the process of getting a divorce.

But in a statement to reporters, Cazeneuve hinted that Bouhlel may have had a last-minute adoption of a more extremist worldview.

โ€œIt seems he was radicalized very quickly,โ€ he said.

The Paris prosecutorโ€™s office said Saturday that five people were in custody following the attack. Neighbors told the Associated Press that Bouhlelโ€™s estranged wife was one of them.

As France began three days of national mourning Saturday, Niceโ€™s seaside Promenade des Anglais slowly and painfully came back to life. A makeshift memorial of bouquets, candles and messages was set up near one end of the expansive avenue.

Yet the suffering is far from over. Two days after the atrocity, some families were still hunting for missing loved ones, going from hospital to hospital to find relatives who had disappeared in the bloody chaos of the truckโ€™s rampage.

Officials said 202 people had been wounded in the attack, including many children. The local childrenโ€™s hospital said of the 30 minors brought for treatment after the attack, two had died, one was in critical condition, and three were on artificial respiration.

The dead included six of seven members of one extended family โ€“ three generations โ€“ from northeastern France who had gathered in Nice to celebrate Bastille Day and each otherโ€™s company.

Government spokesman Stephane Le Foll warned against attempts to divide the country, calling for โ€œunity and cohesion.โ€ Still, the message was heard, prompting the security announcement later from Cazeneuve.

France is facing a general election next year, and the deeply unpopular Hollande is facing multiple challengers, from within his own Socialist Party, from the right-wing Republicans and from the far-right National Front.