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The prominent Russia opposition leader Alexei Navalny is back in prison to finish his 30-day sentence after being taken to the hospital following a severe allergic reaction on Sunday, the same day Moscow's citizens took to the streets to protest local election authorities for disqualifying independent candidates from the Moscow city council ballots. Navalny was in jail for calling the protests.

Navalny's lawyer, Olga Mikhailova, said he has "gotten better after an intense treatment," but she remains "categorically" opposed to his return to prison while it remains unclear what caused the reaction — Navalny reportedly had no known allergies before Sunday. Mikhailova added that there was no consultation with a toxicologist or any toxicological test results.

Navalny's personal doctor said that Navalny was "poisoned by some sort of unknown chemical substance," backing up Mikhailova's concerns, Deutsche Welle reports.

Radio Free Europe/Radio Liberty reports that while the lack of clarity has raised such speculation, Leonid Volkov, one of Navalny's top aides, rejected conspiracy theories and instead criticized the standard hygiene standards at the detentions center. Volkov said he had a similar reaction when he was held in the same cell as Navalny last month.

Sunday's protests resulted in police detaining more than 1,300 demonstrators after a violent crackdown. Russia courts began sentencing the protesters on Monday.