A female teacher has been stabbed to death in front of her pupils at a primary school in the southern French town of Albi by a student's mother, who was immediately detained.
"This morning, a mother showed up with a knife and stabbed a 34-year-old teacher in front of her students, for reasons that will be determined by the investigation," Albi prosecutor Claude Derens said.
"When I arrived at the scene they were trying to revive her. She was in cardiac arrest in her classroom," he said.
President Francois Hollande immediately sent Education Minister Benoit Hamon to the school to take charge of the government response.
"All state services will be mobilised to take care of these children and the staff who witnessed this awful tragedy," Mr Hollande said in a statement.
The stabbing took place as morning classes began at Albi's Edouard Herriot primary school, which is attended by 284 students aged from three to 11.
No further details were immediately available and a press conference is planned for this afternoon.
A spokesman for Mr Hamon said he was on his way to the school to show his support, saying the education minister "is deeply shocked by this crime, which plunges the end of the school year into mourning."
"This tragedy confirms there is a need to fight against violence in and around schools, to protect schools, teachers and students."
The incident comes amid concerns in France over assaults by parents on teachers.
A study released in April said nearly half of primary school principals had been verbally or physically abused by parents.