France on Saturday said it will deploy 7,000 soldiers after declaring a top-level alert following the fatal stabbing of a teacher by a Chechen-origin man, who also severely wounded three others at a school.

The attack took place in the northeastern town of Arras, home to large Jewish and Muslim populations.

Police arrested the suspected attacker, Mohammed Moguchkov, who had cried the Arabic phrase "Allahu akbar!" (God is greatest), according to the preliminary elements of the investigation.

Authorities have suggested a probable link to the ongoing violence in the Middle East, with President Emmanuel Macron denouncing the incident as an act of "Islamist terror".

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 with 10,000 soldiers and 4,700 police and gendarmes deployed since the aftermath of the January 2015 attacks to protect parts of the country deemed sensitive from terrorism.

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

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

According to the interior ministry, the president 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 upped its alert level to the highest position following a crunch security meeting chaired by Macron on Friday, the prime minister's office told AFP.

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, who is in his 20s, 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.

- 'Terrorism has struck' -

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

Among those wounded were a school security guard 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, according to anti-terror prosecutor Jean-Francois Ricard.

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

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 17-year-old brother was detained close to another school.

- Panic in school -

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

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

Martin Dousseau, a philosophy teacher who witnessed the attack, described a moment of panic during break-time, when 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," Dousseau said.

"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, claimed by the Islamic State group (IS), on targets in Paris where 130 people were killed.

There has been a relative lull in recent years, though 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.

Speaking in Arras, he 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 Paris and other French cities on 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 around 3,000 people present.

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