IS claims Nice massacre as France mulls security failings

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. 

French President Francois Hollande met with his defence and security chiefs and cabinet ministers as criticism from the opposition and media mounted over security failings after the third major attack in France in 18 months.

"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.

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.

Hollande said the country would observe three days of mourning as he warned the death toll could rise further, with more than 50 people still fighting for their lives.

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 attack.