The French government said on Tuesday it planned to create a new offence of endangering people by publishing their personal details on social media, following the beheading of a teacher.
The announcement came as the authorities ordered the closure of a Paris mosque that posted a video criticising the teacher for discussing cartoons of the Prophet Mohammed in a class on free speech.
Social media played a pivotal role in inciting the murder of Samuel Paty, a 47-year-old history teacher, according to sources close to the investigation.
It emerged on Tuesday that the killer, an 18-year-old Chechen refugee, exchanged WhatsApp messages with a parent leading an online campaign to get Mr Paty fired.
Brahim Chnina, whose daughter attends Mr Paty's school, had posted videos identifying the teacher and is one of 16 people under arrest over the killing.
Marlène Schiappa, a junior interior minister, met senior executives of social media platforms including Facebook, Twitter and Snapchat on Tuesday to discuss ways of combating what she called "cyber-Islamism".
Jean Castex, the prime minister, said in parliament: "We cannot reconcile ourselves to impassively witnessing outpourings of hate on social media."
He said the government would put forward a bill to outlaw endangerment on social media and make platforms more accountable for content. It will be an amended version of an earlier bill banning hate posts passed by parliament but overturned by France's Constitutional Council in June.
Four schoolchildren who are among those being held over the killing have reportedly admitted being paid more than €300 (£270) by the killer, Abdoullakh Anzorov, to tell him where to find Mr Paty.
They said Anzorov, who was shot dead by police, told them he wanted Mr Paty to apologise for using the cartoons. The children said they had no idea he was planning the murder.
President Emmanuel Macron is clamping down on Islamist groups and several are expected to be banned. He is under pressure to halt Islamist attacks, which have killed more than 240 people since 2015.
A tribute to Mr Paty will be held at the Sorbonne University in Paris on Wednesday. The teacher, who was the father of a five-year-old boy, will be posthumously awarded the Légion d'honneur.