According to a substitute prosecutor at the Tunisian anti-terrorism prosecutor's office, a group called Al Mehdi of Southern Tunisia, previously unknown to Tunisian authorities, claimed responsibility for the terror attack.
The suspected knifeman, identified as Brahim Issaou, was shot multiple times by police in the aftermath of the attack.
The exact motive of the attack was unclear but comes as France is under alert for Islamic extremist acts amid tensions over caricatures of the Muslim Prophet Mohammed published by satirical French weekly Charlie Hebdo, and after two other recent attacks in France with links to the cartoons.
"You don't know the French language, you don't know anyone there, you're going to live alone there, why, why did you go there?" she said she told him over the phone at the time.
Though many other young men in their area have made that journey, his family said Aouissaoui had not told them of any specific plans, though he had spoken before about wanting to go to Europe.
Macron on Thursday urged people of all religions to unite and not "give in to the spirit of division".
The 47-year-old is believed to have been in contact with Aouissaoui the night before the attack.
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The French government has designated it as a terrorist attack.
The attack occurred at around 9 a.m. (0800 GMT) at the Notre-Dame basilica in the heart of the city of Nice, news channel BFMTV reported.
France's chief anti-terrorism prosecutor, Jean-Francois Ricard, said the suspect was a Tunisian born in 1999 who arrived in Europe on September 20 in Lampedusa, the Italian island off Tunisia that is a main landing point for migrants from Africa. He condemned the Nice stabbings, but said Western leaders also bore responsibility for such crimes due to their roles in Middle East conflicts.
Issaoui was shot by police multiple times and is now in grave condition at a hospital.
Police said Saturday a third man, aged 33, was arrested after being present when the home of the second suspect was raided.
Several Muslim-majority countries have launched campaigns to boycott French products, while protesters burnt the French flag and posters of Macron as demonstrations were held in Syria, Libya, Bangladesh, Afghanistan, Pakistan and the Palestinian territories.
After arriving in Nice at around dawn on Thursday, he spent about an hour and a half in the train station, then put on new shoes and reversed his coat, the French prosecutor said. The teacher had showed caricatures of Prophet Muhammad in class before the attack.
But some claim Macron is unfairly targeting France's estimated five to six million Muslims - the largest community in Europe.