Controversial French comedian Dieudonné M'bala M'bala has been detained by police for a Facebook comment appearing to back Paris gunman Amedy Coulibaly, reports BBC News.
His is one of dozens of cases opened by authorities in a crackdown on condoning or threatening terrorism.
Justice minister Christiane Taubira said words of hatred and contempt had to be fought with the "utmost vigour".
Dieudonné already has convictions for inciting anti-Semitism and the courts banned several one-man shows last year.
The justice ministry said on Wednesday that 54 cases had been opened since the murders of 17 people in Paris last week. Of those, 37 cases involved condoning terrorism and 12 were for threatening to carry out terrorist acts.
Some fast-track custodial sentences have already been handed down under anti-terror legislation passed last November:
- A man of 22 was jailed on Tuesday for a year for posting a video mocking one of the three murdered policemen
- A drunk driver was given four years in prison after making threats against the police who arrested him
- Three men in their twenties were jailed in Toulouse for condoning terrorism
- A man of 20 was jailed in Orleans for shouting "long live the Kalash[nikov]" at police in a shopping centre
The justice minister said prosecutors should act firmly and quickly against anyone found condoning terrorism or carrying out racist or anti-Semitic acts.
Dieudonné is already facing an inquiry into whether he condoned terrorism in a video in which he mocked the decapitation of US journalist James Foley by Islamic State militants.
If found guilty, he could face up to seven years in jail and a 5,000-euro (£3,800; $5,900) fine.
Hours after 3.7 million people took part in rallies across France on Sunday, with the biggest in the centre of Paris, Dieudonné said on his Facebook page that the "historic" march had been as magical as the Big Bang that had created the universe.
"I'm finally going home," he wrote. "Know that this evening, as far as I'm concerned, I'm feeling like Charlie Coulibaly [in French: je me sens Charlie Coulibaly]."
He combined the "Je suis Charlie" ("I am Charlie") slogan adopted across the world in support of the 17 victims of the Paris attacks with the name of one of the three Paris gunmen, before deleting the remark a short time later.
Coulibaly killed a policewoman near a Jewish school last Thursday before going on to hold up a kosher supermarket the following day when he murdered four Jewish hostages.
Read more of this report from BBC News.
See also:
Why we unite against anti-Semitic comedian Dieudonné - but don't want to ban him
Why controversial French comic Dieudonné is forming a new political party