MOSCOW—Hundreds of thousands rallied in the capital of Chechnya on Monday after the Kremlin-backed leader there declared a holiday to denounce the French magazine Charlie Hebdo’s caricatures of the Muslim Prophet Muhammad.

Russia’s Interior Ministry said more than 800,000 people from the mainly Muslim republics along its southern rim joined the rally in Grozny, the Chechen capital. Though Russian officials often overestimate numbers at such events, media shots of the crowd showed what looked like hundreds of thousands of people packing the city center.

Members of Russia’s Orthodox clergy joined the march, denouncing the West for “trying to sow discord between our religions,” Russian state-controlled news agencies said. Others carried signs reading “Hands off the Prophet Muhammad” in a rally billed as a “love for the Prophet Muhammad” event.

The rally comes as the Kremlin is struggling to calm Islamist sentiment within its borders that it fears could become radicalized by the rise of the extremist group Islamic State in Iraq and Syria.

Although Moscow sent its foreign minister to Paris to join a solidarity march in the wake of the attacks on Charlie Hebdo, the Kremlin has made it clear that no similar satire of Islam would be allowed in Russia.