Russian police detained Alexei Navalny for less than an hour Thursday, the prominent opposition leader tweeted Thursday. Navalny said that during the brief arrest, which came just as he was leaving a dental appointment, officials warned him that he faces up to 30 days in prison for organizing illegal protests.

"They offered me a lift somewhere," he said, according to a translation by Reuters, "but I declined and have gone to work. I don't understand what happened, and why it took seven people to detain me."

It is not the first time the 41-year-old critic of the Kremlin has run afoul of Russian authorities this year. Just last month, Navalny got wrestled to the ground during widespread protests calling for a boycott of the March 18 presidential election — an election the anti-corruption campaigner has been barred from running in, after he was convicted of fraud in a case widely viewed as politically motivated.

"I'm definitely not alone, and I'm not some kind of dissident," he told NPR's Lucian Kim earlier this month. "If you take any of my anti-corruption investigations or any points from my political platform, I'm sure the majority of Russian citizens would support me — and that's why I wasn't allowed to run."

As Lucian notes, his says it has already attracted more than 200,000 volunteers and opened dozens of offices across the country.

It's unlikely the election will be anything but a victory lap for President Vladimir Putin, who has held power in Russia for 18 years and claims approval ratings north of 80 percent.

Still, Putin's critics point to his rough treatment of the opposition as evidence his support is built on authoritarian practices — including the arrest of Navalny's chief of staff, Leonid Volkov, who tweeted Thursday that he had also been detained shortly before Navalny was.

Reuters, citing Navalny's spokeswoman, reports that Volkov remains in police custody after he was picked up at Moscow's Sheremetyevo International Airport.

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