France will deploy 7,000 soldiers after a Chechen-origin man fatally stabbed a teacher and severely wounded three other adults at a school in the northeastern town of Arras, the Elysee presidential palace said Saturday.
The attack on Friday was denounced by President Emmanuel Macron as an act of "Islamist terror" in Arras, which has large Jewish and Muslim populations.
The deployment of the soldiers will be completed by Monday evening.
France has raised its alert level to the highest position following a crunch security meeting chaired by Macron on Friday.
Macron said a separate "attempted attack" in another region had been foiled by security forces.
"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.
The suspected attacker, Mohammed Moguchkov, who is in his 20s, was arrested by police.
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.