French authorities said Tuesday they would close a Paris mosque as part of a clampdown on radical Islam that has yielded over a dozen arrests following the beheading of a teacher who had shown his pupils a cartoon of the Prophet Mohammed.

The mosque in a densely-populated suburb northeast of Paris had disseminated a video on its Facebook page days before Friday's gruesome murder, railing against teacher Samuel Paty's choice of material for a class discussion, said a source close to the investigation.

The interior ministry said the mosque in Pantin, which has some 1,500 worshipers, would be shut on Wednesday night for six months.

Interior Minister Gerald Darmanin, who vowed Monday there would be "not a minute's respite for enemies of the Republic," had asked regional authorities to carry out the mosque closure.

The head of the Pantin mosque, M'hammed Henniche, explained on Tuesday he had shared the video not to "validate" the complaint about the cartoon, but out of concern for Muslim children being singled out in class.

The school said Paty had offered Muslim pupils the choice to leave the classroom before showing a cartoon of the prophet naked.

Meanwhile, the police on Monday raided Islamic associations and individuals suspected of extremist religious beliefs, arresting dozens of people, in a sweep expected to last a few more days.

Darmanin said there were some 80 investigations being conducted into hate speech online and that he was looking into whether to disband some 51 associations within the Muslim community.

The associations included the Collective against Islamophobia in France (known by the French acronym CCIF) and the humanitarian association BarakaCity.

In a statement on the group's Facebook page, BarakaCity slammed the move: "Madness has seized the interior minister who, because he cannot find anything against our NGO, has taken advantage of the emotion caused by this tragedy."

The political temperature is also rising, with French President Emmanuel Macron promising that "fear is about to change sides" in a new anti-Islamist campaign.

Far-right National Rally leader Marine Le Pen – likely to face Macron in a 2022 presidential election – has called for "wartime legislation" and an immediate moratorium on immigration.

The spillover of religious tensions

French teachers have long complained of tensions around religion and identity spilling over into the classroom.

Samuel Paty, 47, was attacked on his way home from the junior high school where he taught in Conflans-Sainte-Honorine, 40 kilometers northwest of Paris.

A photo of the teacher and a message confessing to his murder was found on the mobile phone of his killer, 18-year-old Chechen Abdullakh Anzorov, who also posted images of the decapitated body on Twitter.

The murder was preceded by a fierce online campaign against Paty and the school, led by the father of a schoolgirl who accused the teacher of disseminating "pornography" for showing a cartoon of the prophet naked.

The father who posted the video shared by the Pantin mosque is among 15 people arrested after the killing, along with a known Islamist radical and four members of Anzorov's family.

Four pupils suspected of accepting payment for pointing Paty out to his killer were also in custody Monday.

Tens of thousands of people took part in rallies countrywide on Sunday to honor Paty and defend freedom of expression. 

Within the rally, some held placards reading "I am Samuel" that echoed the "I am Charlie" rallying cry after the 2015 attack on the satirical newspaper Charlie Hebdo. 12 people, including cartoonists, were gunned down for publishing cartoons of Mohammed.

Another silent rally is being planned for Tuesday evening in homage to Paty, and Macron will attend a ceremony organized with the teacher's family on Wednesday.

(With input from AFP)