Paris: The teacher who was beheaded in a street in France had received threats after showing controversial cartoons of Prophet Muhammad to his pupils, French media reported.
He has been identified as 47-year-old Samuel Paty, a history and geography teacher.
Nine people have been arrested, including the parents of a child at Paty's school, judicial sources were quoted as saying.
Police say the attacker was an 18-year-old man of Chechen origin.
The killing took place while a trial is underway in Paris in a 2015 Islamist assault on the French satirical magazine Charlie Hebdo, which was targeted for publishing the cartoons, the BBC reported.
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.
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The attack occurred at about 15:00 (GMT) near the College du Bois d'Aulne, where he taught, in the town of Conflans-Sainte-Honorine, some 30 km (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".