Prime Minister Manuel Valls today called the man who rammed his truck into the crowd in Nice a 'terrorist' with probable links to radical Islam.
At least 10 children and teenagers were among the dead, mown down as Mohamed Lahouaiej-Bouhlel ploughed his lorry through the festive crowd of thousands watching fireworks for France's national day last night.
Anti-terrorism prosecutor Francois Molins said the Tunisian attacker was "completely unknown" to the intelligence services but that the assault was "exactly in line with" calls from jihadist groups to kill.
As France was left reeling from its third major attack within 18 months, President Francois Hollande warned that the toll could rise further, with more than 50 people fighting for their lives.
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The attack left a scene of carnage on Nice's picturesque Promenade des Anglais, with mangled bodies strewn over the palm-fringed walkway.
AFP reporter Robert Holloway witnessed the white truck driving at speed into the crowd, causing "absolute chaos".
"It was hurtling towards us and we had just enough time to yell at each other 'get out of the way!'," he said.
The massacre again prompted questions as to why France is such a persistent target for such attacks and what can be done to prevent such an unsophisticated assault.
Hollande's political opponents were already pointing the finger, with presidential contender Alain Juppe saying the carnage could have been avoided if "all measures" had been taken.
Hollande said many foreigners were among the dead and injured in what he described as a "terrorist attack".
"France was struck on its national day... The symbol of freedom," the president said in a sombre televised address.
A Texas-based newspaper, the Austin American-Statesman, named the American victims as Sean Copeland, 51, and his 11-year-old son Brodie.
Hollande said France would observe three days of national mourning from tomorrow and Paris city hall said the Eiffel Tower was to be lit in France's national colours today in tribute to the victims.