The latest suspect was arrested following Thursday's church attack in Nice in which at least three people were stabbed to death.
A new suspect is in custody in the investigation into a gruesome attack by a Tunisian man who killed three people in a French church that prompted France to heighten its security alert amid existing religious and geopolitical tensions around cartoons mocking Prophet Muhammad.
The suspect is a 47-year-old man believed to have been in contact with the attacker the night before the attack on the Notre Dame Basilica in the Riviera city of Nice, according to a judicial official. The official was not authorised to be publicly named.
The attacker, Ibrahim Issaoui, was seriously wounded by police and hospitalised in life-threatening condition, authorities said. Anti-terrorism prosecutors in France and Tunisia are investigating.
In an interview broadcast Friday with Saudi-owned Al-Arabiya TV, Issaoui's mother said she was shocked by the events.
From the Tunisian province of Sfax, the mother, her eyes wet with tears, said she was surprised to hear her son was in France when he called upon his arrival and had no idea what he was planning.
“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.
His brother told Al-Arabiya that Issaoui had informed the family he would sleep in front of the church and sent them a photograph showing him at the cathedral where the attack took place.
“He didn’t tell me anything,” he said. A neighbour said he knew the assailant when he was a mechanic and held various other odd jobs, and had shown no signs of radicalisation.
France’s anti-terrorism prosecutor said the suspect is a Tunisian born in 1999 who reached the Italian island of Lampedusa, a key landing point for migrants crossing in boats from North Africa, on September 20 and travelled to Bari, a port city in southern Italy, on October 9.
It is not clear when he arrived in Nice.
France's anti-terror prosecutor Jean-Francois Ricard said Aouissaoui was in a "life-threatening" condition.
The victims were "targeted for the sole reason that they were present in this church at that moment," Ricard said at a press conference late Thursday.
President Emmanuel Macron said he would immediately increase the number of soldiers deployed to protect schools and religious sites from around 3,000 to 7,000.
Macron, who travelled to the scene, denounced it as an "Islamist terrorist attack" and said France would not cave to terror over his vow to combat extremist violence.
Authorities have closed some mosques and shut down two groups accused of fomenting hate and violence in the wake of Paty's killing, which prompted an outpouring of anger that saw thousands of people demonstrate across France last weekend.
The controversial cartoons
More than 250 people have been killed in attacks on French soil since January 2015, when gunmen massacred 12 people at the offices of Charlie Hebdo over its publishing of cartoons of Prophet Muhammad.
Depicting prophets is strictly avoided in Islam.
Muslims object to the cartoons on the basis that they were meant to provoke and insult the community at large. The publication of such caricatures is seen in the larger context of the French state's anti-Islam policies which have discriminated against people for eating Halal food and women wear the hijab.
To mark the start of the trial for 14 suspected accomplices of the attackers, Hebdo republished the controversial cartoons last month.
Just days later, an 18-year-old man from Pakistan seriously injured two people with a meat cleaver outside Hebdo's former offices in Paris.
On October 16, school teacher Samuel Paty was beheaded for showing Hebdo's caricatures of Prophet Muhammad to his students in a class on civics.
But Macron's attitude towards Islam in France and his defence of the cartoons, has outraged many Muslims around the world who accuse him of unfairly targeting an entire religion. Protests have continued in several Muslim countries, demanding France stop mocking Islam by allowing the publication of Prophet Muhammad's caricatures.
Several countries have called for a boycott of French goods, with Turkish President Erdogan leading the charge.
French Foreign Minister Jean-Yves Le Drian insisted on Thursday that France extended "a message of peace to the Muslim world" Thursday, saying it was a "country of tolerance".
Many French imams have also appealed for calm.
"Today I feel like a Christian because this touches the very heart of a man or woman," Otmane Aissaoui, imam at the ar-Rahma mosque in Nice, said after the attack Thursday.
"Islam, like Christianity or Judaism, is light-years away from an act like this," he said.