The French interior minister has called on “all patriotic citizens” to become reservists to boost security in the wake of the attack in Nice, in which 84 people were killed.

Bernard Cazeneuve reiterated that France would call up 12,000 reservists.

Mohamed Lahouaiej-Bouhlel drove a lorry into crowds marking Bastille Day on the Promenade des Anglais on Thursday, before he was shot dead by police.

So-called Islamic State claimed one of its followers carried out the attack.

A news agency linked to the group, Amaq Agency, said: “He did the attack in response to calls to target the citizens of the coalition that is fighting the Islamic State.”

Five people believed to be linked to Lahouaiej-Bouhlel, including his estranged wife, are in police custody, the Paris prosecutor’s office said.

France, which on Saturday began three days of mourning, already has 120,000 police and military deployed around the country. Its 12,000 reservists are made up of 9,000 military police officers and a further 3,000 regular police officers.

“I want to call on all French patriots who wish to do so, to join this operational reserve,” Mr Cazeneuve said.

Some 30,000 people were on the Promenade des Anglais at the time of the attack on Thursday night.

Of the 84 who died, 10 were children. A total of 303 people had been taken into hospital following the attacks, the French health department confirmed on Saturday. Of those, 121 remain in hospital, 30 of whom are children, and 26 people are still in intensive care – including five children.

Residents of Nice and foreign tourists were killed, among them four French citizens, three Algerians, a teacher and two schoolchildren from Germany, three Tunisians, two Swiss, two Americans, a Ukrainian, an Armenian and a Russian.

Previously, Mr Cazeneuve said Lahouaiej-Bouhlel seemed to have been “radicalised very quickly”, urging that this was a “new type of attack…[and] showed the extreme difficulty of the fight against terrorism”.

Lahouaiej-Bouhlel, a 31-year-old Tunisian, drove the lorry 2km (1.2 miles) along the promenade, at times zig-zagging to target people, prosecutors said.

French President Francois Hollande met with his defence and security chiefs and cabinet ministers on Saturday and called for national unity in France.

He said: "We are in a time when, and we have seen it, there is a temptation to divide the country.

“Faced with these temptations, faced with this risk, we must recall the unity and cohesion of this country.”