ISIS says it carried out Nice truck attack
Islamic State has claimed it carried out the Nice truck attack which killed at least 84 people, in a statement carried by the group's media outlet.
Five people have been arrested following the Bastille Day massacre, according to officials.
Inquiries were continuing into whether 31-year-old driver Mohamed Lahouaiej Bouhlel acted alone or had accomplices before he drove a 19-tonne hired truck into scores of people.
More than 200 people on the Promenade des Anglais were injured.
Officers carried out a raid at an address near Nice's main train station on Saturday morning and made two arrests, Europe 1 reported. They were thought to be known to the killer.
A third person was also arrested at an address in Nice earlier in the morning.
According to reports, the terrorist's ex-wife was being questioned on Friday.
The driver's father has reported that Bouhlel had received psychiatric treatment in the past.
He was unknown to the security services.
The Queen added her voice to the wave of sympathy from leaders across the world as the country faced another terrorist attack, following those in Paris in November, in which 130 died, and in January 2015 in which 17 were killed.
President Francois Hollande said 50 people were "between life and death", while several people were among the missing and a "small number" of Britons were injured.
The Foreign Office on Friday night described the carnage as a "terrorist attack", causing multiple casualties, and updated its advice for Britons in Nice.
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."
A vigil took place at Nice Cathedral on Friday night and mourners also gathered at a makeshift memorial amid a visible police presence near the promenade, which is closed to the public.
Revellers in the resort initially thought the commotion was part of a celebratory firework display, but then saw the lorry and assumed the driver had lost control.
Jan Jeffreys and her partner Les Smith, from Shropshire, were enjoying their first evening in Nice when the attack happened.
They described a chaotic scene as people tried to run out of harm's way.
Ms Jeffreys, 53, told the Press Association: "There were people in cars turning round on grass verges, reversing. It was just mayhem."
Mr Smith said he was haunted by images of bodies lying in the street.
The 63-year-old businessman said: "The first body that I saw was covered in a sheet and was quite obviously a heavily pregnant woman. It was very upsetting. I keep seeing it. I just can't understand why this happened."
Another couple from Dungannon, Co Tyrone, said they saw a mood of celebration turn to one of fear as they watched the tragedy unfold from their holiday apartment balcony.
Philip Rodgers, 67, in the city with his wife Yvonne, described "tremendous fireworks, crowds and crowds of lovely families, then panic. Very, very frightening". He said it went from "pure happiness to fear".
Prime Minister Theresa May has said Britain must redouble its efforts to defeat "brutal" terrorist "murderers", while police forces across England and Wales have been told to review security at major events over the next week in the wake of the bloodbath.
Foreign Secretary Boris Johnson, who had celebrated Bastille Day with dinner at the French embassy in London, described the attack as "appalling and cowardly".
The Association of British Travel Agents (Abta) issued a statement encouraging people to check with their tour operators before heading to France.
There was a lengthy queue for passport control as passengers landed at Nice airport on flights from London on Friday evening.
In a tribute to the victims of the attack, the first night of the BBC Proms opened with the French national anthem.
The BBC Symphony Orchestra played La Marseillaise to a packed Royal Albert Hall.