Mayor Estrosi’s tweet said: “I am on site with the @PoliceNat06 and the @pmdenice who arrested the perpetrator of the attack. I confirm that everything suggests a terrorist attack in the Basilica of Notre-Dame de #Nice06 .”
The attack comes while France is still reeling from the beheading earlier this month of French middle school teacher Samuel Paty in Paris by a man of Chechen origin.
The attacker had said he wanted to punish Paty for showing pupils cartoons of the Prophet Mohammad in a civics lesson.
A motive for the Nice attack was not immediately clear, or if there was any connection to the cartoons, which Muslims consider to be blasphemous.
Since Paty’s killing, French officials – backed by many ordinary citizens – have re-asserted the right to display the cartoons, and the images have been widely displayed at marches in solidarity with the killed teacher.
That has prompted an outpouring of anger in parts of the Muslim world, with some governments accusing French leader Emmanuel Macron of pursuing an anti-Islam agenda.