By Pascal Rossignol, Layli Foroudi and Michel Rose
ARRAS, France (Reuters) -A 20-year-old knifeman fatally stabbed a teacher in an attack at a school in the northern France city of Arras on Friday that President Emmanuel Macron condemned as "barbaric Islamic terrorism".
Two other people were seriously wounded and fighting for their lives, Macron said after visiting the school.
"The teacher who was killed stepped in and undoubtedly saved a lot of lives himself," Macron said after paying his respects to the dead teacher, whose body still lay under a cover and surrounded by a pool of blood.
Saying the school would reopen on Saturday, he added: "Our choice is made not to give in to terror, not to let anything divide us."
In a national address a day earlier, Macron had urged the French to remain united and refrain from bringing the Israel-Hamas conflict home.
He stopped short of making a direct link in Arras but said: "Terrorism strikes once again in a school, and in a context that we all know."
The suspect, who has been arrested, was a former student of the Lycee Gambetta high school where the attack happened, a police source said. One of the attackers' brothers was also detained nearby.
The investigation was handed to the anti-terrorism prosecutor's office.
Police could not confirm local media reports that Friday's attacker shouted "Allahu Akbar".
But the attacker was on a state watchlist of people known as a potential security risk, a police source said. The "Fiche S" contains thousands of names and only a small number are actively monitored.
He was described by the police source as a Russian-born Chechen but by some French media as a Russian-born Ingush.
A security source said an elder brother of the alleged assailant was serving time in prison for links to Islamist militant networks and glorification of terrorist acts.
France has been targeted by a series of Islamist attacks over the years, the worst being a simultaneous assault by gunmen and suicide bombers on entertainment venues and cafes in Paris in November 2015.
In 2020, a teacher, Samuel Paty, was beheaded by a Chechen teenager who wanted to avenge his use of cartoons mocking the Prophet Mohammad during a class on freedom of expression.
"Once again a school was hit by the barbarity of Islamic terrorism," Macron said.
A video obtained by Reuters showed three people - one of them with a chair - trying to stop the attacker in the school's parking lot and getting struck by him. "He's got a knife, he's got a knife," one of those watching the scene said.
"We're all in a state of shock," said philosophy teacher Martin Doussau, who was chased down by the attacker but managed to escape unharmed after locking himself in a room.
Doussau said he witnessed the assailant going after the school's cook in the yard during a break between two classes before the attacker approached his way.
"It's when I left that I discovered that one of our colleagues had been stabbed in the carotid artery and died in front of the school," he told Reuters.
A security alert was triggered later at another school in Arras, a school worker told Reuters. A third man was arrested in that incident, when he tried to enter the school with a suspicious backpack, French media reported.
Education Minister Gabriel Attal said security would be reinforced in schools throughout France.
Macron said another attack had been prevented on Friday in the wider Paris region.
Witnesses said the attacker did not appear to be wanting to settle a grudge.
"He was looking for a history teacher," teacher Doussau said. "That's what leaves me thinking this wasn't related to a personal problem, or about settling a personal vendetta with a teacher."
Pupils were confined to their classrooms for hours.
Louis, a 15-year-old pupil, said students initially assumed it was a drill, when the alarm rung and they had to hide.
"I'm shocked that this happened here. ... It shows it can happen anywhere," he told Reuters.
Arras is a city in the de-industrialised, ethnically diverse northern corner of France, a region where the far right enjoys strong support.
(Reporting by Pascal Rossignol and Ardee Napolitano in Arras and Michel Rose, Layli Foroudi, Charlotte Van Campenhout, Tassilo Hummel, Benoit van Overstraeten, Blandine Henault in Paris; Writing by Ingrid Melander; editing by Richard Lough, Deborah Kyvrikosaios and Jonathan Oatis)