Church bells will toll across the country, and the country will fall silent at midday, a now grimly familiar ritual after the third major terror attack in 18 months on French soil.
French investigators have yet to find links between attacker Mohamed Lahouaiej-Bouhlel, a 31-year-old Tunisian, and the Islamic State group which claimed responsibility for the carnage, Interior Minister Bernard Cazeneuve told France's RTL radio.
"We cannot exclude that an unbalanced and very violent individual" has been "through a rapid radicalisation, committed to this absolutely despicable crime," he said.
Lahouaiej-Bouhlel was shot dead after zigzagging a 19-tonne truck through a crowd of tourists, locals and families enjoying a fireworks display in the Riviera city of Nice on Bastille Day.
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Mangled bodies were left strewn across the Riviera city's seafront in the grisly attack by a man described by those who knew him as a loner with a history of violence and depression.
The attack comes eight months after IS jihadists killed 130 people across Paris, and 18 months after three days of terror at the Charlie Hebdo weekly and a Jewish supermarket killed 17.
"We are at war, outright war. So I will use strong words: it will be us or them," he said.
While previous attacks saw grand displays of national unity, any semblance of cohesion quickly unravelled after the Nice massacre and Sarkozy joins a long line of opposition politicians who have criticised the government.
Cazeneuve described the politicians as "shameful".
"Certain members of the political class have not respected
the mourning period. Arguments broke out right away which personally saddens and shocks me," he said.
"Enough with the speeches" and "Sick of carnage in our streets," the messages read.
The government has sought to fend off criticism, assuring that security at the Bastille Day event was high and scrambling to reassure citizens about their safety.