French police have raided the homes of dozens of suspected Islamic radicals following the beheading of a teacher who showed controversial cartoons of the Prophet Muhammad to his pupils.
Some of those being questioned are believed to have posted messages of support for the killer of Samuel Paty.
The government also said it was probing 51 French Muslim associations.
Paty's suspected killer was shot dead by police on Saturday after the attack close to the teacher's school.
The school is located in Conflans-Sainte-Honorine, a north-western suburb of Paris.
The suspect, an 18-year-old born in Moscow of Chechen origin, had no known connection to Paty or the school.
Dozens post messages supporting killer
On Monday, Interior Minister Gérald Darmanin said the latest raids sent a message that there was "no respite for enemies of the republic", and that they were expected to continue all week.
He said that not all individuals targeted in the operations were necessarily linked to the investigations into Paty's death.
Meanwhile, police will interview about 80 people who are believed to have posted messages in support of Paty's killer, Darmanin added.
The government said that if Muslim organisations under investigation were found to promote hatred, they would be closed down.
Darmanin labelled one organisation, the Collective Against Islamophobia in France (CCIF), an "enemy of the state", and said he wanted to shut it down.
The organisation, which monitors anti-Muslim hate crime in France, has accused Darmanin of slander after he claimed the group was "obviously" involved in the attack, according to AFP news agency.
In a statement following news of the attack, the CCIF expressed "our pain and our sadness to the family of this teacher".
What's the latest in the investigation?
Anti-terrorism prosecutor Jean-François Ricard said Paty had been the target of threats since he showed the cartoons of the Prophet Muhammad during a class about freedom of speech.
As he had done in similar lessons in recent years, Paty, a history and geography teacher, advised Muslim students to look away if they thought they might be offended.
Depictions of the Prophet Muhammad can cause serious offence to Muslims because Islamic tradition explicitly forbids images of Muhammad and Allah (God).
The issue is particularly sensitive in France because of the famous publishing of cartoons of Prophet Muhammad by satirical magazine Charlie Hebdo. A trial is currently underway over the killing of 12 people by Islamist extremists at the magazine offices in 2015.
Some French-Muslims say they are frequent targets of racism and discrimination because of their faith - an issue that has long caused tension in the country.
Eleven people have been arrested as part of the police investigation into Paty's murder. No more information on the arrests is available.
Shock among French citizens
The attack has shocked and horrified France. Thousands gathered at weekend rallies to honour Paty with people carrying placards reading "Je suis enseignant" (I am a teacher).
Muslim leaders in France have condemned the attack. "A civilisation does not kill an innocent person, barbarism does," Tareq Oubrou, imam of a mosque in Bordeaux, told France Inter.
The Strasbourg-based Assembly of Chechens in Europe said in a statement: "Like all French people, our community is horrified by this incident."
President Emmanuel Macron said the attack bore all the hallmarks of an "Islamist terrorist attack" and the teacher had been murdered because he "taught freedom of expression".
Islamists would not be allowed to sleep quietly in France, Macron was quoted as saying in a cabinet meeting on Sunday.
Ricard said that the suspect, who lived in the Normandy town of Évreux, about 100km from the murder scene, went to Paty's school in Conflans-Sainte-Honorine and asked students to point out the teacher.
The suspect followed Paty as he walked home from work. He then used a knife to attack the teacher in the head, and then beheaded him.
Witnesses are said to have heard the attacker shout "Allahu Akbar", or "God is Greatest".
As police approached him, he fired at them with an airgun. Officers returned fire, hitting him nine times. A 30cm-long blade was found close by.
Authorities said the man had been before courts but only on minor misdemeanour charges.