Macron arrived early Thursday afternoon in Nice at the scene of the attack.
"Once more, France has been attacked. Three of our compatriots have died...for values that we hold dear, the value of freedom," said the president defiantly.
"I say again clearly today: we will not give up our values."
The attack in the southern city is France's third suspected jihadist rampage in just over a month.
France raised its national security alert level to "attack emergency" – the top of the five-point terror scale from "no threat" to "imminent risk of serious attack".
Prime Minister Jean Castex said Thursday's assault, in which one woman was reportedly beheaded, was "as cowardly as it is barbaric". Castex told parliament he had decided to raise France's Vigipirate security alert system to the highest.
Le Gouvernement vient de porter le plan Vigipirate au niveau urgence attentat sur l'ensemble du territoire.
— Jean Castex (@JeanCASTEX) October 29, 2020
Le président de la République a convoqué demain matin un Conseil de défense et de sécurité nationale.
This status, colour-coded scarlet, has been declared on only three previous occasions: after the killings at a Jewish school near Toulouse in 2012, after the Charlie Hebdo killings in 2015, and in the wake of the Bataclan attack, also in 2015, when a generalised scarlet alert formed part of the national state of emergency.
Immediately after Thursday's attack, French Interior Minister Gerald Darmanin ordered the reinforcement of police and army patrols at places of worship and cemeteries.
Solidarity from French Muslim council
The president of the French Council for the Muslim Faith condemned the murders. Speaking to France Info, Mohammed Moussaoui called for Muslims to show solidarity with the victims, asking them to cancel celebrations for Thursday's Mawlid holiday, commemorating the birth of Prophet Mohammed.
The president of the French Council for the Muslim Faith #CFCM, #MohammedMoussaoui condemns the #Nice attack, calls for today's celebrations of the #Mawlid holiday, marking the birth of Prophet Mohammed, to be cancelled in solidarity with the victimshttps://t.co/P7bGQwEVtf
— RFI English (@RFI_En) October 29, 2020
The leader of the Roman Catholic Church, Pope Francis, prayed for the victims of the attack, as the Vatican said "terrorism and violence can never be accepted".
"Today's attack has sown death in a place of love and consolation. The Pope is aware of the situation and is close to the mourning Catholic community," Vatican spokesman Matteo Bruni said in a statement.
The Pope "prays for the victims and their loved ones, so that the violence may cease, so that we may return to look upon ourselves as brothers and sisters and not as enemies, so that the beloved French people may unite to combat evil with good", he said.
Knife attacker shot in Avignon
Police sources have meanwhile confirmed that a man wielding a knife was shot dead by security officers in the southern French city of Avignon.
French broadcaster @Europe1 reports that around 11:15 this morning, police shot dead a man in #Avignon after he threatened people with a knife, shouting "God is greatest" in Arabichttps://t.co/uo5Co31558
— RFI English (@RFI_En) October 29, 2020
At 11:15 on Thursday morning, police were confronted a man carrying a knife. When he refused to drop his weapon, he was flash-balled but continued to advance. Officers then used their handguns and the suspect died on the spot.
An internal police investigation has been launched.
The authorities say they are remaining open-minded about the possible motivation of the dead man but, for the moment, have no reason to suspect him of attempting a terrorist crime.
