Well-known opposition blogger in Russia Yegor Zhukov was beaten in Moscow and taken to hospital for treatment.
Police have launched a criminal investigation into the attack.
His supporters posted a photo on Facebook of his bloodied and swollen face. The attack took place near his home on Sunday night, they said.
In December, 22-year-old Zhukov was given a three-year suspended sentence for “incitement to extremism”
He told investigators that “two unidentified men attacked him on Rashchupkin Street and injured him,” a police statement was quoted as saying by Interfax.
Kremlin spokesman Dmitry Peskov said police were investigating the attack, adding: “Hopefully, the perpetrators will be identified and punished in accordance with the law.”
Now Mr. Zhukov is also a political commentator on Russian radio. He was arrested last August during protests against the exclusion of independent and opposition candidates from the council elections in Moscow.
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Earlier on Sunday, Mr Zhukov said on his YouTube channel that he had been rejected for a master’s degree in cinema at Moscow’s prestigious Higher School of Economics after he was initially accepted. He linked this rejection to this political activity.
Separately, Mr Peskov, a Kremlin spokesman, said he was opposed to linking the attack to the alleged poisoning of Russia’s most prominent participant in President Vladimir Putin, investigative blogger Alexei Navalny.
Germany’s concern for Navalny
Mr Navalny remains in intensive care in an induced coma in Germany suffering from suspected nerve poisoning.
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Germany has called on Russia to do more to clarify the alleged poisoning. Mr Navalny was deported from Russia nine days ago. On Friday, the hospital said he was in serious but stable condition.
His supporters believe he was poisoned by a cup of tea he drank at Tomsk airport in Siberia before boarding a flight.
Commenting on relations with Russia, German Foreign Minister Heiko Maas said they were under “dark clouds”.
“Sanctions remain in place and will continue until the basis for them changes. And there are dark clouds at the moment, and of course we expect Russia to contribute more to clarifying the Navalny case than it is now.”