French police on Sunday arrested two more people in connection with Thursday's bombing in Nice that killed 84 Bastille Day celebrants, bringing the total number of those detained to seven.
Authorities say a man and a woman were the latest arrests. Police gave no information on why they were detained.
The Islamic State terror group claimed responsibility for the attack in a statement published in an IS media outlet, calling the attacker a "soldier."
It remained unclear whether there was any direct connection between the French-Tunisian attacker and the terrorist group. However, France's interior minister said Saturday that it appeared that Mohamed Laouaij Bouhlel "was radicalized very quickly."
Bernard Cazeneuve said that based on the initial testimony of those who knew Bouhlel, "he did not show himself over the years ... as having a link to radical Islamist ideology."
The French prosecutor's office did not provide details about the latest arrests.
France began the first of three days of national mourning Saturday for those killed in the holiday attack. Ten children were among the 84 fatalities; two U.S. citizens were also confirmed to be among the dead. More than 200 people were injured, 52 of those critically, before police were able to fatally shoot the attacker.
Bouhlel, 31, who lived in Nice, was suspected by local police to have committed criminal offenses. In March, he was given a suspended six-month sentence for armed violence that had taken place in January.
Bouhlel was divorced and had three children. His father, interviewed by Agence France-Presse in Msaken, Tunisia, said his son had problems from 2002 to 2004 "that caused a nervous breakdown."
'Facing a struggle'
In an address to the nation, French President Francois Hollande said the attack was done "to satisfy the cruelty of an individual and maybe a group." Speaking after visiting the hospital where victims were treated, he also said France was "facing a struggle which will be long.''
U.S. President Barack Obama said the United States would stand with France and had offered assistance in the investigation. The U.S. leader praised France for its "extraordinary resilience and democratic values that have made France an inspiration to the entire world." He also urged Americans to believe in the values of freedom of religion and added that Americans and allies could not give in to fear, turn on each other or sacrifice “our way of life.”
“We will not be deterred. We will not relent. We are going to keep working together to prevent attacks and defend our homeland. We are going to keep taking out ISIL leaders and pushing ISIL back in Syria and Iraq," Obama said, using an acronym for Islamic State. "We’re going to keep standing with our partners from Africa to Afghanistan, and we are going to destroy this vile terrorist organization."
Hollande said France's state of emergency, set to end later this month, would be extended another three months. He also extended Operation Sentinel, which was introduced after terror attacks in January 2015 and allowed 10,000 extra military personnel to boost the ranks of security forces across the country. He said France would strengthen its roles in Syria and Iraq. "We will continue striking those who attack us on our own soil," Hollande said.
Nice, France's fifth-largest city and the capital of the Cote d'Azur region, was put on lockdown by security forces in case further attacks might be planned.
Thursday's slaughter was the third major terrorist attack in France since last year. A coordinated attack in Paris on November 13 killed at least 130 people in a strike claimed by Islamic State, and a series of attacks in January 2015 that began with an assault on the offices of the satirical magazine Charlie Hebdo killed 17 people.