In a statement via its Amaq news service IS said one of its "soldiers" carried out the attack on Thursday night "in response to calls to target nations of coalition states that are fighting (IS)".
Tunisian Mohamed Lahouaiej-Bouhlel, 31, smashed a 19-tonne truck into crowd of people in the Riviera city who were celebrating Bastille Day -- France's national day. Police said he had no known connection to jihadist groups.
"If we are at war, as the government tells us, then the currency of war is intelligence, learning from experience, analysing failures and victories," wrote Yann Marec in an editorial for the southern region's Midi Libre newspaper.
He was one of several calling for action, and not merely "the same old solemn declarations" from the government, as Le Figaro daily said.
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Some 30,000 people had thronged the palm tree-lined Promenade des Anglais on Thursday night to watch a fireworks display with their friends and families, but the night turned to horror as the truck left mangled bodies strewn in its wake.
Four more people linked to Lahouaiej-Bouhlel have been arrested. The driver's estranged wife is also being held by police.
IS also claimed responsibility for November 13 attacks in which 130 people were killed in Paris, while gunmen in January 2015 attacks on the Charlie Hebdo weekly and a Jewish supermarket were linked to both IS and Al-Qaeda.
The massacre has once again shaken the country to its core, and prompted questions about the effectiveness of security measures with the country already under an eight month-long state of emergency.
Presidential contender and former prime minister Alain Juppe said yesterday that the latest carnage could have been prevented if "all measures" had been taken.
But government spokesman Stephane Le Foll slammed Juppe's comments, saying there was as much security present for the fireworks display as there had been for the Euro 2016 football tournament in the city.
He said there were more than 185 police, gendarmes and soldiers on the ground, as well as municipal police and a vast network of surveillance cameras.