A French schoolboy on Friday died from wounds sustained in a violent assault, as President Emmanuel Macron warned schools should be protected from "uninhibited violence" among some youths.

The 15-year-old teenager was badly beaten Thursday near his school in a town south of Paris and rushed to hospital following a cardiac arrest.

He died of his wounds early on Friday afternoon, a prosecutor said.

It was the second such assault this week, after a 13-year-old girl was left temporarily comatose after being attacked outside her school in the southern city of Montpellier on Tuesday.

Both incidents come at a time of heightened tensions around French schools after threats of attacks were sent to dozens of educational establishments via an internal messaging system.

"We have a form of uninhibited violence among our teenagers and sometimes among increasingly younger ones," Macron said earlier in the day as he visited a primary school in Paris.

"Schools need to be shielded from this," he said, adding they should "remain a sanctuary for our children, for their families, for our teachers."

"We will be intransigent against all forms of violence," he said. He however added it was now up to the investigators to shed light on both incidents.

- 'Barbaric' -

In the latest beating, several people attacked the 15-year-old as he left school Thursday afternoon in a low-income district of Viry-Chatillon, a town around 20 kilometers (12 miles) south of Paris.

The schoolboy suffered cardiorespiratory arrest, a police source said.

He was rushed to a top paediatric hospital in Paris, according to Jean-Marie Vilain, the mayor of Viry-Chatillon.

He said the boy was set upon as he walked home after a music class, accusing the assailants of being "the worst kind of thugs".

"This extreme violence is becoming commonplace," he added.

Government spokeswoman Prisca Thevenot denounced what she called a "barbaric crime".

Another police source said three youths wearing balaclavas assaulted the boy in the hall of a building.

No arrests had been made, but police were examining CCTV footage.

The public prosecutor's office said it was conducting a probe into murder and gang assault.

Outside the school on Friday morning, before the boy died, fellow students said they were shocked he was attacked.

The schoolboy, identified as Shamseddine, "got on well with everyone", said one female pupil who asked to remain anonymous.

A football under his arm, 12-year-old Matheo, another student, said he was scared the attackers would come back.

 Social media insult? 

 On Tuesday, a teenage girl was attacked outside her school in the southern city of Montpellier.

Prosecutors said the girl, identified as Samara, had emerged from a coma but was "seriously injured".

Three alleged attackers, including a girl from the same school in the city's low-income area of La Mosson-La Paillade, have been arrested on suspicion of attempted murder of a minor.

"Each of them admits to having hit the victim," prosecutor Fabrice Belargent said on Friday, adding the oldest of the three -- a 15-year-old -- would remain in temporary detention.

"It seems the assault came in the context of a group of teenagers who were used to insulting each other on social media," Belargent said.

He did not refer to religion as a factor.

Samara's mother had told media that her 13-year-old daughter had been bullied by a fellow pupil, raising the possibility this could have been over her behavior and clothing being deemed un-Islamic.

But fellow pupils at the school on Thursday said the girl who took part in the assault had accused Samara of posting a picture of her with an insult on social media.