Dozens of suspected Islamist extremists are being investigated in connection with the beheading of a teacher in Northern Paris. France's Interior Minister said the father of a pupil had issued a fatwa against the victim.

French police have launched operations against "dozens of individuals" suspected of having links to radical Islam following the decapitation of a French schoolteacher, Interior Minister Gerald Darmanin said Monday.

History teacher Samuel Paty was beheaded on Friday outside his school on Paris' Northern outskirts after showing his pupils cartoons of the Prophet Muhammad. His attacker, an 18-year-old Chechen, was shot dead by police shortly after the attack. 

The gruesome killing shocked France and prompted weekend protests across the country in support of freedom of speech. 

Darmanin told Europe 1 radio that about 80 police investigations were underway into online hate messages that glorified the attack.

"There have already been arrests since Sunday. Since this morning, police operations have taken place and more will take place, concerning dozens of individuals," he said.

Authorities also targeting suspect organizations  

Darmanin said that more than 50 associations were being probed as part of the ongoing operations.

He said he was also looking into whether certain groups in the French Muslim community that had been accused of promoting violence should be dissolved. He named the nongovernmental organization BarakaCity and the Collective Against Islamophobia in France (CCIF) as two possible candidates.

A police source cited by the Reuters news agency on Sunday said that France was preparing to expel 231 foreigners on a government watch-list for suspected extremist religious beliefs. However, it was not clear whether that development was linked to Monday's operations.

Freedom of speech

Friday's attack came after Paty showed his students cartoons of the Prophet Muhammad as part of a class discussion about freedom of speech. The 47-year-old teacher had been the target of online threats as a result of his lesson plan.

Darmanin said the father of a schoolgirl and a known Islamist had "apparently launched a fatwa against the teacher." The two men are among 11 people currently in police custody. 

The 18-year-old attacker was a Russian-born refugee living northwest of Paris. He was not previously known to police.