A teacher has been beheaded in a suburb north-west of the French capital Paris, reports say, with the attacker shot dead by police.
The victim in Conflans-Sainte-Honorine was a teacher who showed caricatures of the Prophet Muhammad in a classroom, media reports say.
The anti-terrorist prosecutor has been called in to lead an investigation.
Interior Minister Gerald Darmanin, travelling to Morocco, is returning urgently to Paris.
The attack occurred at about 17:00 local time (15:00 GMT) near a school.
France’s AFP news agency, quoting police and prosecutors, said the victim had been decapitated.
A man wielding a large knife attacked the teacher, cutting off his head. The attacker then ran off, but local police alerted by the public were quickly at the scene.
When they shouted at him to give himself up he issued threats so they shot him and he died a short time after, in the nearby area of Éragny.
The scene is now sealed off, as the investigation continues.
In a tweet (in French), police urged members of the public to avoid the area.
The trial is under way in Paris of alleged accomplices in the deadly 2015 attack on the satirical magazine Charlie Hebdo, which had published cartoons of Prophet Muhammad.