The suspected knifeman stormed the Gambetta-Carnot High School in the northern city of Arras late on Friday morning, authorities say.
According to local media, he shouted ‘God is great’ in Arabic before stabbing two teachers and a security worker, leaving one of the teachers fatally wounded.
The suspect, who has been named as 20-year-old Mohammed Mogouchkov, used to be a pupil at the school and was on a watchlist of known threats to national security, according to police sources cited in French reports.
He was described as being of Chechen origin, a majority-Muslim ethnic group concentrated in the Russian republic of Chechnya.
France’s president, Emmanuel Macron, described the incident as an act of ‘barbaric Islamic terrorism’.
The national terror threat level has been raised and local authorities have been ordered to ramp up security at all schools.
Later on Friday, a 24-year-old man on the same terror watchlist, was arrested while carrying a knife just outside a high school hundreds of kilometres away in Limay.
The teacher who died in Arras, 50-year-old French language teacher Dominique Bernard, ‘came forward to protect others and without doubt saved many lives’, Macron added.
Footage shared on social media appeared to show a confrontation in a courtyard at the heart of the school, which teaches pupils aged 15 to 18.
In one clip, a man in dark clothing and white trainers is seen aggressively stalking a man near a pair of parked vehicles while another man watches from nearby.
In another video, shot from a high-up window, the same man in white trainers is seen attacking two men, including one wielding a chair, who approached him along with two others.
A voice near the person filming is heard exclaiming: ‘They’re fighting! He has a chair, he has knives.
Another says: ‘He has a knife, guys, he has a knife.’
Martin Doussau, a philosophy teacher at the school who confronted the attacker, said he was wielding two-knives and believes he had a ‘political’ motive.
He told BFM TV: ‘It lasted around 10 minutes. When I saw that this person was attacking the head cook, I went towards him to ask him to stop.
‘When he turned to ask if I was a history teacher, I understood this was a political act. I don’t think he was looking for one person in particular.
Mr Doussau separately told Reuters the attack ended in a ‘relatively peaceful manner’ when police stunned the suspect with what appeared to be a taser.
Both the suspect and his brother have been arrested, according to French Interior Minister Gérald Darmanin.
No pupils are believed to have been injured in the attack, which triggered an emergency lockdown and evacuation of the premises.
The two injured were said to be in ‘extremely’ critical condition, with one havingsuffered a wound to an artery in the neck.
Mr Darmanin and France’s president, Emmanuel Macron, were scheduled to visit Arras later on Friday in solidarity with the survivors.
A number of French politicians made references to the 2020 beheading of 47-year-old teacher Samuel Paty outside his school in Conflans-Sainte-Honorine.
His murderer, Abdoullakh Anzorov, also a Russian immigrant of Chechen origin, had been enraged by a social media frenzy surrounding the showing of a cartoon of the Prophet Muhammad in one of Mr Paty’s classes.
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