Navalny's allies said on Wednesday that they were concerned by a deterioration in his health and his lawyers said they had not been allowed to visit him in prison.
Russia's FSIN prison authority confirmed that officers had detained the prominent critic of President Vladimir Putin, the Interfax news agency reported.
The announcement came as the European Union’s top diplomat told Russia’s foreign minister that the treatment of Navalny represents "a low point” in the relations between Brussels and Moscow.
For a decade, Russian President Vladimir Putin has avoided putting his gadfly opponent Alexey Navalny behind bars for any considerable length of time — until Tuesday, when a Moscow court ordered Navalny to spend the next two-and-a-half years in prison.
Volkov has urged Russians to gather near their homes for a brief Valentine’s Day protest this weekend, shining their mobile phone torches and lighting candles in heart shapes to flood social media.
Navalny, President Vladimir Putin’s most prominent critic, was jailed earlier this month for parole violations he said were trumped up. The West has condemned the case and is discussing possible sanctions on Russia.
“The EU needs to send a very clear and decisive message that this is not acceptable,” Gabrielius Landsbergis said in a video statement, calling for more sanctions on Russian individuals.
Three European diplomats told Reuters on Thursday that the European Union was likely to impose travel bans and asset freezes on allies of Russian President Vladimir Putin, possibly as soon as this month, after France and Germany signalled their willingness to move ahead.
Russian police said on Friday that they would ask Germany to allow their officers to question opposition leader Alexei Navalny, who is being treated in Berlin for poisoning.