The anti-Kremlin activist fell ill earlier this week shortly after he was interviewed by Al Jazeera.

Pyotr Verzilov, a prominent anti-Kremlin activist and member of the Pussy Riot protest band, has been flown to Berlin for treatment after falling sick with a mysterious illness.

The 30-year-old suddenly fell ill several days ago shortly after an interview with Al Jazeera and has since had trouble seeing, speaking, and moving.

Those close to Verzilov suspect he has been poisoned.

Images posted on Twitter by Pussy Riot member Nadezhda Tolokonnikova, who is also his ex-wife, show Verzilov arriving in Germany on Sunday, where an ambulance was waiting for him.

An official account for Pussy Riot posted a picture promising to “punish those who poisoned Verzilov”.

The anti-Kremlin feminist punk band stages regular protests against the Russian government.

right now at riot fest pic.twitter.com/Ud6uvmFYIQ — 𝖕𝖚𝖘𝖘𝖞 𝖗𝖎𝖔𝖙 (@pussyrrriot) September 14, 2018

Verzilov garnered attention earlier this year when he and three female members of the protest group staged a brief pitch invasion during the FIFA World Cup final in Moscow in July.

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The group served a 15-day sentence for running onto the pitch in front of President Vladimir Putin and other high-ranking officials wearing police uniforms.

The stunt was meant to promote free speech, the group said.

Verzilov is also the publisher of Mediazona, a Russian online news outlet which focuses on human rights violations inside the country’s penal system.

“There’s no criminal justice system here. In any democratic country, the main criteria of a criminal justice system is its independence. In Russia, it is just the department of internal affairs of the president’s administration which follows the orders of these or that people in power,” Verzilov told Al Jazeera shortly before he fell ill.

“Our goal is to … show what’s wrong and how you can fight it.”

Pussy Riot rose to prominence in 2012 when its members were jailed for staging a protest against Putin in a Russian Orthodox cathedral in Moscow.

The group has since become a symbol of anti-Kremlin protest action.