France's national anti-terror prosecutors said on Thursday they have opened a murder inquiry after a man killed three people , including one whose throat was slit, at a basilica in central Nice and wounded several others.
The city's mayor, Christian Estrosi, told journalists at the scene that the assailant, detained shortly afterwards by police, "kept repeating 'Allahu Akbar' (God is Greater) even while under medication".
He added that President Emmanuel Macron would be arriving shortly in Nice.
"The situation is now under control," police spokesperson Florence Gavello said.
Nice mayor Christian Estrosi said on Twitter, "I can confirm everything lets us think this was a terror attack in the Notre-Dame Basilica," in central Nice.
France has been on high alert for terror attacks since the 15 January massacre at the satirical weekly Charlie Hebdo, and the trial of suspected accomplices in that attack is currently underway in Paris.
A wave of jihadist attacks on French soil, often by so-called "lone wolf" assailants, has killed more than 250 people since 2015.
The assault prompted lawmakers in parliament to hold a minute of silence, before Prime Minister Jean Castex and other ministers abruptly left for an emergency meeting with President Emmanuel Macron.