The prosecutor’s office in Moscow asked the court to recognize as “extremist” the song of the rapper Oxxxymiron, one of the most popular Russian musicians, who publicly opposed the invasion of Ukraine, Russian news agencies reported with reference to Reuters.

A spokesman for the Moscow prosecutor’s office said that investigators are studying the “justification of acts of violence and the ideology of violence” in one of Oxxxymiron’s songs, Interfax reports.

According to Russian law, materials marked as “extremist” are prohibited.

Oxxxymiron, whose real name is Myron Fedorov, has been one of the country’s most prominent rappers for a decade, gaining notoriety for his politically charged lyrics that often target the Kremlin.

Shortly after Russia’s invasion of Ukraine on February 24, Oxxxymiron canceled a planned tour in Russia, saying, “I can’t entertain you when Russian missiles are falling on Ukraine.”

He later left Russia, holding a series of concerts in Istanbul, London and Berlin called “Russians against the war”, the proceeds of which were intended for Ukrainian refugees.

Russian rappers have been under the watchful eye of the Kremlin before. In April, Ivan Dryomin, under the pseudonym Face, was declared a “foreign agent” after a public speech against the war in Ukraine.