The man suspected of killing three people at a church in the southern French city of Nice on Thursday is a 21-year-old Tunisian who arrived in Europe just a few weeks ago, sources close to the inquiry said.
The suspect, identified as Brahim Aoussaoui, landed in late September on the Italian island of Lampedusa, where he was placed in virus quarantine by authorities before being released with an order to quit Italian territory.
He arrived in France in early October, the sources said.
Meanwhile, French President Emmanuel Macron said on Thursday that he would be stepping up the deployment of soldiers to protect key French sites, such as places of worship and schools, following the fatal knife attack in Nice earlier in the day.
France has raised the security alert for French territory to the highest level after the knife attack in the city of Nice, Prime Minister Jean Castex said on Thursday.
Castex also told French National Assembly that the government's response to the attack would be firm and implacable.
Meanwhile, European Union leaders expressed solidarity with France on Thursday and pledged to confront "those that seek to incite and spread hatred" after a knifeman killed three in a Nice church.
"I condemn the odious and brutal attack that has just taken place in Nice and I am with France with all my heart," European Commission president Ursula von der Leyen tweeted.
"My thoughts are with the victims of this hateful act. All of Europe is in solidarity with France. We wil remain united and determined in the face of barbarity and fanaticism."
Charles Michel, the president of the European Council, dubbed the attack "abominable" and declared: All of Europe is with you."
And David Sassoli, speaker of the European Parliament, said: "We have a duty to stand together against violence and those that seek to incite and spread hatred."
A man wielding a knife at a church in the French city of Nice killed three people, slitting the throat of at least one, and injured several others before being apprehended by police, officials said Thursday.
French anti-terror prosecutors have opened an inquiry into what the city's Mayor Christian Estrosi called an "Islamo-fascist attack."
"He (the attacker) kept repeating 'Allahu Akbar' (God is Greater) even while under medication" after he was injured during his arrest, Estrosi told journalists at the scene.
Two victims died at the Basilica of Notre-Dame, in the heart of the city on the Mediterranean coast, while a third person died of injuries after seeking refuge in a nearby bar, a police source told AFP.
"The situation is now under control," police spokeswoman Florence Gavello said.
France has been on high alert for terror attacks since the January 2015 massacre at the satirical weekly Charlie Hebdo. The trial of suspected accomplices in that attack is under way in Paris.
In Nice in particular, painful memories remain fresh of the attack during the Bastille Day fireworks on July 14, 2016, when a man rammed his truck into a crowded promenade, killing 86 people.
It was part of a wave of attacks on French soil, often by so-called "lone wolf" assailants, which has killed more than 250 people since 2015.
The assault prompted lawmakers in parliament to hold a minute's silence on Thursday, before Prime Minister Jean Castex and other ministers abruptly left for an emergency meeting with President Emmanuel Macron.
Estrosi, who said Macron would soon be arriving in Nice, called for churches around the country to be given added security or to be closed as a precaution.
The attack comes just days after thousands rallied across France in solidarity with a teacher beheaded for showing pupils cartoons of the Prophet Mohammed.
The history teacher, Samuel Paty, was killed by an 18-year-old Chechen man, Abdullakh Anzorov, who committed the gruesome crime outside Paty's school in a Paris suburb after the teacher was denounced by angry parents on social media.
His murder prompted Macron to promise a crackdown in extremism, including shutting down mosques and organisations accused of fomenting radicalism and violence.
But the move has inflamed tensions with many Muslims saying Macron is unfairly targeting France's estimated five to six million Muslims - the largest community in Europe.
Protests against France have erupted in several Muslim countries, with some urging a boycott of French goods, and tensions have flared in particular between Macron and Turkey's President Recep Tayyip Erdogan.
- October 29: A man bursts into a church in the southern city of Nice, killing three people and injuring several others before being shot and arrested by police.
- October 16: A teacher is decapitated near a school on the outskirts of Paris. The assailant is shot dead by police. Prosecutors say they are treating the incident as "a murder linked to a terrorist organisation". Police say the victim had recently shown caricatures of the Prophet Mohammed in class.
- September 25: A man armed with a knife seriously wounds two people in a suspected terror attack outside the former offices of French satirical weekly Charlie Hebdo in Paris, three weeks into the trial of men accused of being accomplices in the 2015 massacre of the newspaper's staff.
- April 4: In southeastern Romans-sur-Isere, a riverside town, a 33-year-old Sudanese refugee goes on a stabbing spree in broad daylight, killing two people. After the rampage the assailant is arrested without a fight and prosecutors launch an investigation into "murder linked to a terrorist enterprise" and "association with terrorist wrongdoers".
- January 4: A knife-wielding man runs amok in a park south of Paris, killing a man walking with his wife and wounding two other people before being shot dead by police.
Anti-terror investigators take over the probe following evidence that 22-year-old Nathan C. had recently converted to Islam.
- October 3: Mickael Harpon, a 45-year-old computer expert in the Paris police intelligence-gathering department, uses a kitchen knife and an oyster shucker to kill four colleagues. His 30-minute rampage ends when an officer shoots him dead. It emerges that Harpon had converted to Islam about 10 years previously and had connections in the ultra-conservative Salafist movement.
- May 12: Khamzat Azimov, 20, a naturalised Frenchman of Chechen origin, stabs to death a 29-year-old man in Paris' busy Opera district before being shot dead by police. The Islamic State (IS) group claims responsibility.
- October 1: A 29-year-old Tunisian kills two young women with a knife at the main train station in the southern city of Marseille. He is shot dead by soldiers and IS claims his attack.
- July 26: Two teenagers slit the throat of an 85-year-old priest in front of worshippers in a church in the western town of Saint-Etienne-du-Rouvray.
The 19-year-olds are killed by police and their act claimed by the IS group to whom they had sworn allegiance in a video.
- June 13: A 25-year-old uses a knife to kill a police officer and his partner at their home in Magnanville, west of Paris, in front of their young son. He is killed by a police SWAT team but has already claimed the murders on social media in the name of IS.
- June 26: A 35-year-old attacker beheads his boss and displays the severed head at Saint-Quentin-Fallavier in southeastern France. He commits suicide in his jail cell.