French Prime Minister Manuel Valls has been booed as he attended a minute’s silence in Nice, where an attacker in a lorry killed 84 people on Thursday.
Hecklers shouted out “murderer” and “resign” at him before the minute’s silence, held across the nation.
Earlier, centre-right opposition leader Nicolas Sarkozy accused the government of failing to provide security.
Troops are to be redeployed to tourist spots as inquiries continue into the killer’s possible links to jihadists.
Sarkozy, a former president, called for any foreign nationals with links to radical Islam to be expelled from France.
Interior Minister Bernard Cazeneuve said the investigation had not yet found evidence linking attacker Mohamed Lahouaiej Bouhlel to terrorist networks.
The authorities say Lahouaiej-Bouhlel, a Tunisian living in Nice, became radicalised only recently, reports the BBC.
While the so-called Islamic State (IS) group claimed the attack, Lahouaiej-Bouhlel may not necessarily have coordinated it with a larger network, Cazeneuve said.
Many of the dead and injured were children watching a Bastille Day fireworks display with their families.
Dozens of people remain in hospital after the attack.
Neighbours have described Bouhlel as a violent loner who liked to drink, lift weights and go salsa dancing.
