French anti-terror prosecutors said they were treating the assault as "a murder linked to a terrorist organisation" and related to a "criminal association with terrorists".
French police have shot dead a suspect after a history teacher was beheaded in the northwest of capital Paris, authorities said.
The French anti-terrorism prosecutor opened an investigation for murder with a suspected terrorist motive, the prosecutor's office said.
Authorities said the teacher was attacked after he opened a discussion with students on caricatures of Islam’s Prophet Muhammad.
The killing of the teacher in a middle school occurred in the town of Conflans-Sainte-Honorine while the suspect was killed by police in adjoining Eragny. The towns are located in the Val d’Oise region northwest of Paris.
President Emmanuel Macron called the incident a terrorist attack after visiting the school.
Suspect not yet identified
Heavily armed police sealed off the area around the school, and police vans and emergency vehicles lined leafy adjacent streets, according to an Associated Press reporter at the scene.
The suspect’s identity was not made public. French media reported that the suspect was an 18-year-old Chechen, born in Moscow. That information could not be immediately confirmed.
The attack came as Macron is pushing for a new law against what he calls domestic “separatism,” notably by radicals accused of indoctrinating vulnerable people through home schools, extremist preaching and other activities.
A police official said the suspect, armed with a knife and an airsoft gun — which fires plastic pellets — was shot dead about 600 meters (yards) from where the male teacher was killed after he failed to respond to orders to put down his arms, and acted in a threatening manner.
The teacher had received threats after opening a discussion “for a debate” about the caricatures about 10 days ago, the police official told The Associated Press.
The parent of a student had filed a complaint against the teacher, another police official said, adding that the suspected killer did not have a child at the school.
The two officials could not be named because they were not authorised to discuss ongoing investigations.
“We didn't see this coming,” Conflans resident Remi Tell said on CNews TV station. He had attended the middle school where the teacher taught, Bois D'Aulne, and described the town as peaceful.
It was the second terrorism-related incident since the opening of an ongoing trial on the newsroom massacre in January 2015 at the satirical newspaper Charlie Hebdo after the publication of caricatures of the prophet of Islam.