Updated 19:25

France was on high alert on Saturday, after an attacker stabbed a teacher to death in what the president called an act of "Islamist terror," with troops deployed and major attractions including the Louvre museum and Palace of Versailles evacuating visitors.

A Chechen-origin man fatally stabbed a teacher and severely wounded three other adults Friday at a school in northeastern France, with authorities suggesting a probable link to the ongoing violence in the Middle East.

The attack, denounced by President Emmanuel Macron as an act of "Islamist terror", was in the town of Arras which has large Jewish and Muslim populations. 

"This school was struck by the barbarity of Islamist terrorism," Macron said after visiting the school, saying the victim had "probably saved many lives" with his courage in seeking to block the attacker. 

Macron said another "attempted attack" in another region had been foiled by security forces. 

According to the interior ministry, he was referring to the arrest of a "radicalised" man who was arrested leaving a prayer hall in the Yvelines region of Paris for carrying a prohibited weapon.

Interior Minister Gerald Darmanin later said there was "probably a link between what's happening in the Middle East and this incident" in Arras.

France has upped its alert level to the highest position following a crunch security meeting chaired by Macron later Friday, the prime minister's office told AFP.

The suspected attacker, Mohammed Moguchkov, who is in his 20s, was arrested by police. 

A total of eight people were in police custody on Friday, a police source said. 

In addition to the attacker, several members of his family were arrested "for the purposes of the investigation", including one of his brothers and his sister, other police sources said.

The national anti-terrorist prosecutor announced that it has opened an investigation.

Moguchkov is from Russia's mainly Muslim southern Caucasus region of Chechnya. He was already on a French national register known as "Fiche S" as a potential security threat, a police source told AFP, and under electronic and physical surveillance by France's domestic intelligence agency, the DGSI.

Moguchkov cried the Arabic phrase "Allahu akbar!" (God is greatest), according to the preliminary elements of the investigation.

'Terrorism has struck'

The victim, a French teacher, was stabbed in the throat and chest.

Among those wounded were a school security agent who was stabbed multiple times and is fighting for his life, and a teacher in a less serious condition, the source added. 

A cleaner was also hurt, anti-terror prosecutor Jean-Francois Ricard said. 

No pupils at the school were hurt, said another police source. 

The attack comes almost three years to the day after the October 16, 2020 beheading of teacher Samuel Paty, also by a Chechen, near his school in a Paris suburb.

"Three years after the assassination of Samuel Paty, terrorism has struck a school again and in a context that we all know," Macron said.

Police say Moguchkov's brother, aged 17, was detained close to another school. 

Panic in school

The pupils and teachers were confined to the school premises before being allowed out later in the afternoon.

A large security cordon was set up around the school, where the police, firefighters and emergency services were deployed, AFP journalists said. 

Parents gathered in front of the school, where the pupils were visible through the windows.

A philosophy teacher who witnessed the attack, Martin Dousseau, described a moment of panic during break-time, when the schoolchildren found themselves face-to-face with the armed man. 

"He attacked canteen staff. I wanted to go down to intervene, he turned to me, chased me and asked me if I was a history and geography teacher," said Dousseau. 

"We barricaded ourselves in, then the police arrived and immobilised him." 

France has suffered a series of attacks by Islamist extremists since 2015 including the suicide and gun attacks in November 2015 on targets in Paris claimed by Islamic State (IS) that killed 130 people.

There has been a relative lull in recent years, even as officials have warned that the threat remains. 

Stepped-up-protection

Macron said in an address to the nation on Thursday that 582 religious and cultural facilities in France were receiving stepped-up police protection after the attack by Hamas on Israel.

In Paris, the famous Louvre museum evacuated visitors and closed following a "security" threat.

A spokeswoman for the Louvre, the largest museum in the world, told AFP it had "received a written message stating that there was a risk to the museum and its visitors".

The Palace of Versailles, also a major tourist attraction just outside the capital, was evacuated due to a bomb threat made anonymously online, police sources told AFP. 

The deployment of the soldiers from Operation Sentinelle will be completed by Monday evening, according to the Elysee presidential palace.

Sentinelle is a French military operation involving the deployment of soldiers, police and gendarmes set up in the aftermath of January 2015 attacks to protect parts of the country deemed sensitive from terrorism.

Speaking in Arras, Macron reaffirmed his message from that address for the French to "stand shoulder to shoulder" and "stay united". 

French Education Minister Gabriel Attal said in a message to regional education officials security should be reinforced at schools "without delay". 

Darmanin on Thursday had banned pro-Palestinian demonstrations in France until further notice, on the grounds they "are likely to generate disturbances to public order".

In defiance of his order, several hundred people gathered in central Paris and other French cities late Thursday shouting pro-Palestinian and anti-Israeli slogans, AFP correspondents said.

Police in Paris used tear gas to disperse the protesters, and said they had arrested 10 out of the some 3,000 people present.