Alexei Navalny, Putin opponent, doused with chemicals outside Moscow office

Russian opposition leader and activist Alexei Navalny was briefly hospitalized Thursday after being doused with chemicals for the second time in as many months.

Mr. Navalny, 40, was attacked by an unknown person while getting into a car outside his Moscow office, witnesses told regional media.

The assailant doused the politician with a green antiseptic known in Russia as “zelyonka,” resulting in chemical burns to Mr. Navalny’s right eye, the independent television network Dozhd reported.

“The ambulance came, looked at my dark-green eye, and said that they’re taking me to the hospital,” Mr. Navalny said on social media afterwards. They wrapped up [my head] like it’d been seriously injured. It looks pretty funny, but my eye hurts like hell.”

Mr. Navalny was similarly assaulted with antiseptic last month in the Siberian city of Barnaul, and other vocal critics of Russian President Vladimit Putin have been subjected to identical treatment in the weeks since: Ilya Varmalov, an independent Russian journalist, was attacked with zelyonka, eggs and flour at the Stavropol airport Thursday. Meanwhile, Russian opposition political party Yabloko said a female activist, Natalia Fedorova, was “almost blinded” by a similar assault Friday.

The latest wave of attacks has unfolded as the Kremlin continues to crackdown against protesters opposed to the policies of Russian President Vladimir Putin and Prime Minister Dmitry Medvedev. Mr. Navalny has been involved in orchestrating a series of recent rallies against the current government, and intends to campaign for Mr. Putin’s job in next year’s presidential election. The government has challenged his ability to run, however, and has cited a 2013 criminal conviction as grounds for exclusion.

On Wednesday, meanwhile, the prosecutor’s office in Moscow formally blacklisted three group from the country, including “Open Russia,” a British-based organization that had encouraged individuals to protest the Putin regime. Those groups, according to Moscow, have “threatened the basic principles of the constitutional order of the Russian Federation and the security of the state.”