In the wake of the attack in Nice, former French President Nicolas Sarkozy has criticised the government for not doing enough to provide security.
The centre-right opposition leader called for any foreign nationals with links to radical Islam to be expelled from France.
Eighty-four people died when an attacker ploughed a lorry into people celebrating Bastille Day on Thursday.
A minute of silence has been observed in Nice and other locations.
Eighty-five people remain in hospital, 18 of them in critical condition.
Many survivors are still waiting for news of their loved ones. Only 35 bodies have so far been officially identified.
Prosecutors say painstaking measures are needed to avoid errors of identification.
Speaking to French television, Mr Sarkozy said “Democracy must not be weak, nor simply commemorate. Democracy must say ‘We will win the war’.”
He said he supported stronger measures like expulsion of radicalised Muslims, and electronic tagging for those at risk of radicalisation.
France’s government has said it is at war with violent jihadists.
But a third major attack in 18 months has led to criticism of the country’s leaders.
Radicalised too quickly?
There is no indication that the Nice attacker, Mohamed Lahouaiej-Bouhlel, was a jidhadist.
Neighbours have described him as a violent loner who liked to drink, lift weights and go salsa dancing.
- Nice attack: What we know
- Who were the victims?
- Who was the attacker?
But France’s Prime Minister Manuel Valls has suggested he may have been radicalised too quickly to trigger the authorities’ attention.
He was shot dead by police when his vehicle’s path along the Promenade des Anglais was eventually halted.
French media reported that he researched the route in the days before the attack.
The reports say Lahouaiej-Bouhlel drove through the seafront promenade area of the French city on Tuesday and Wednesday in preparation.
Europe 1 radio said CCTV footage from the days beforehand showed him driving through the area in the lorry, closely observing the scene.
Tunisian security sources have told the BBC he visited Tunisia frequently, most recently eight months ago.
So-called Islamic State said the attacker was acting in response to its calls to target civilians in countries that are part of the anti-IS coalition.
At the scene – By Tom Burridge
An impressive air of normality in much of tourist-packed Nice is deceptive. As well as grief, bewilderment hangs in the sea air.
There are tears, hugs and silence at the mountain of candles, flowers and cuddly toys on the beach promenade, where joggers stop and parents bring young children to read the messages.
A large white banner says: Why children? And, in a child’s handwriting: Why do you want war?
The bloodstains on the tarmac are gradually disappearing. The lampposts the lorry smashed into will be replaced.
But for those who knew or loved the victims, things will never be the same. More armed police and soldiers guarding the streets will serve as a reminder.
Amid the fear and sadness, and the unanswerable questions, defiance acts as a source of comfort.
He will never defeat us, says one message on the promenade. Another reads: Love defeats hate.
Six people are being held in connection with the killings.
The latest arrests, of an Albanian couple who have not been identified, were on Sunday morning, French judicial sources said.
Lahouaiej-Bouhlel’s estranged wife, who was detained on Friday, was released on Sunday.