The man who killed a French schoolteacher last week said he was acting for the Islamic State (IS) group, in a video recorded before the attack, a source close to the case said Tuesday.

Mohammed Moguchkov, 20, also made a "very marginal" reference to the October 7 attack by Hamas on Israel in the video before knifing the teacher to death at a school in Arras in northern France on Friday, the source added.

Moguchkov, a Russian from the mainly Muslim northern Caucasus region, was due to appear before an investigating magistrate later Tuesday to be charged.

The attack came almost three years to the day after a similar killing of a teacher near Paris, which shocked the public and triggered a massive security response.

France again raised its security level after Friday's attack, deploying 7,000 troops. 

Adding to the tension, the school in the town of Arras was evacuated Monday over a bomb threat, which proved to be a false alarm.

Following the shooting in Brussels of two Swedes by a Tunisian man also claiming inspiration from Islamic State, President Emmanuel Macron said Tuesday that "all European states are vulnerable... there is a return of this Islamist terrorism".

"We all have a vulnerability. It's what comes with being a democracy, a rule-of-law state where there are individuals who can decide at a given moment to commit the worst acts," Macron told reporters in Albanian capital Tirana.

He nevertheless added that he had seen "no failures" by French security services ahead of the stabbing in Arras.

- 'Sanctuary' schools -

At home, Macron has told ministers to "embody a state that is ruthless towards all those who harbour hate and terrorist ideologies".

He wrote that schools would remain a "bulwark" against extremism and "a sanctuary for our pupils and everyone who works there" in a Monday post on X (formerly Twitter).

Macron's office said he would attend the funeral of the victim, 57-year-old Dominique Bernard, on Thursday.

The murder has intensified nervousness in France, which has large Muslim and Jewish populations and has been on the alert for violence since Hamas's attack on Israel.

Interior Minister Gerald Darmanin said Monday that 102 people had been arrested for anti-Semitic acts or expressing support for terrorism since the October 7 assault.

Bernard was killed almost three years to the day after teacher Samuel Paty was beheaded outside his school in a Paris suburb, on October 16, 2020.

The families of Paty's killer and the suspected Arras assailant both hail from Russia's North Caucasus region.

Moguchkov was born in the republic of Ingushetia and reportedly arrived in France aged five.

He was already on a French national register as a potential security threat and under surveillance by France's domestic intelligence agency, the DGSI. His father, who was also on the list, was deported in 2018. 

Macron has called on police to comb through their files of radicalised people who could be deported.

Darmanin said 193 such cases would be re-examined.

Macron has told Darmanin to focus especially on "young men between the ages of 16 and 25 from the Caucasus", his aide said.

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