Witnesses had heard the attacker shout “Allahu Akbar”, or “God is Greatest”.

The attacker, who was shot dead by a police patrol, was said to be  a 18-year-old born in Moscow and originating from Chechnya, the predominantly Muslim Russian republic in the North Caucasus.

A man armed with a knife beheaded a school history teacher in front of his school in Conflans Sainte-Honorine, a suburb northwest of Paris. The attack is being treated as terrorism.

The teacher had shown pupils caricatures of the Prophet Mohammad, which are considered by Muslims to be blasphemous.

Witnesses had heard the attacker shout “Allahu Akbar”, or “God is Greatest”.

The attacker was later shot dead by a police patrol a few streets away. Reports said he is a 18-year-old born in Moscow and originating from Chechnya, the predominantly Muslim Russian republic in the North Caucasus.

Five suspects were arrested on Friday night, bringing the total number of people detained in connection to the killing to nine, including the grandparents, parents and 17-year-old brother of the suspected attacker.

Prosecutors said they were treating the attack as “a murder linked to a terrorist organization” and related to a “criminal association with terrorists.”

French President Emmanuel Macron described the incident as an “Islamist terror attack” and urged the nation to unite.

He said the victim was murdered because he was a teacher and taught freedom of expression.

“The whole country stands behind its teachers. Terrorists will not divide France, obscurantism will not win,” Macron said after visiting the scene.

Police officials told the Associated Press that the victim had received threats after opening a discussion “for a debate” about the caricatures about 10 days ago. An official told the news agency that the parent of a student had filed a complaint against the teacher.

The teacher reportedly gave Muslim students the option of leaving the room before showing the images.

Last month, a man of Pakistani origin attacked and wound two people with a meat cleaver outside the offices where the Charlie Hebdo magazine was based at the time of attack in 2015.