The teacher who was beheaded in a street in France had received threats after showing controversial cartoons of the Prophet Muhammad to his pupils, French media report.
Nine people have been arrested, including the parents of a child at the school where the teacher was working, judicial sources are quoted as saying.
The attacker was shot dead by police near the scene of Friday’s killing.
Police say the attacker was an 18-year-old man of Chechen origin.
The killing took place while a trial is under way in Paris over a 2015 Islamist assault on the French satirical magazine Charlie Hebdo, which was targeted for publishing the cartoons.
French President Emmanuel Macron said the attack bore all the hallmarks of an “Islamist terrorist attack” and the teacher had been murdered because he “taught freedom of expression”.
Speaking at the scene hours after the incident, he stressed national unity. “They will not prevail, they will not divide us,” he said.
What do we know?
The attack occurred at about 17:00 (15:00 GMT) near a middle school in the town of Conflans-Sainte-Honorine, some 30km (20 miles) north-west of central Paris.
A man wielding a large knife attacked the teacher in the street, cutting off his head. Witnesses are said to have heard the attacker shout “Allahu Akbar”, or “God is Greatest”.
The attacker then ran off, but local police were quickly at the scene, having been alerted by the public.