French police are questioning nine people in custody after a suspected Islamist sympathiser beheaded a school teacher in broad daylight on the street in a Paris suburb, police have said.
Police shot the attacker dead minutes after he killed 47-year-old history teacher Samuel Paty on Friday.
Investigators were seeking to establish whether he had acted alone or had accomplices. French media reported that he was an 18-year-old of Chechen origin.
Mr Paty had earlier this month shown his pupils cartoons of the Prophet Mohammad in a civics class on freedom of expression, angering a number of Muslim parents.
Muslims believe that any depiction of the Prophet is blasphemous.
Prime Minister Jean Castex said the attack bore the hallmarks of Islamist terrorism and promised his government would respond.
"I want to share with you my total indignation. Secularism, the backbone of the of the French Republic, was targetted in this vile act," Mr Castex said.
Four relatives of the attacker, including a minor, were detained in the immediate aftermath of the attack in the middle-class suburb of Conflans-Sainte-Honorine, according to police sources.
Five more were detained overnight, among them two parents of pupils at the College du Bois d'Aulne where the teacher was employed.
A week earlier, one man who said his daughter was in Mr Paty's class recorded a video shared on social media in which he branded the teacher a thug and appealed to others to "join forces and say 'stop, don't touch our children'".
It was not clear whether the parent was one of those in police custody. It was also not immediately known if the attacker had seen the video.
Parents of pupils laid flowers at the school gate. Some said their children were distraught.
Muslim leaders condemned the killing, which many public figures perceived as an attack on the essence of French statehood and its values of secularism, freedom of worship and freedom of expression.
Tareq Oubrou, the imam of a Bordeaux mosque, said of the killing, "It is not a civilisation that kills an innocent person, it is barbarity".
The litany of deadly attacks by Islamist militants or their sympathisers was devastating for France's Muslim community, Oubrou told France Inter.
"Every day that passes without incident we give thanks," he said.
"We are between hammer and anvil. It attacks the Republic, society, peace and the very essence of religion, which is about togetherness."