MOSCOW -- Russian opposition leader Alexei Navalny was released from jail on Monday at the end of a 30-day sentence for staging an unsanctioned protest -- and then immediately detained again. A police officer approached him and took him away just as he came out of a detention center in Moscow at daybreak to be greeted by supporters and the media.

Navalny has been the driving force behind a recent series of anti-government rallies that were held in dozens of cities and towns across Russia's 11 time zones.

Navalny's spokeswoman, Kira Yarmysh, said on Monday Navalny is facing charges of staging a rally that caused bodily harm to unidentified people.

Get Breaking News Delivered to Your Inbox

Navalny's further detention comes amid a wave of popular discontent against a hike in the retirement age, an issue that angered Russians across the political spectrum.

A drop in approval ratings for President Vladimir Putin and outrage at the changes in the pension system have weighed heavily on Kremlin candidates running in regional elections in Russian regions.

Early results from run-off votes in Sunday's gubernatorial elections in two Russian regions see opposition candidates beating Kremlin incumbents. A week earlier, an opposition candidate for governor in the Far East mounted protests following widespread reports of vote-rigging in favor of the Kremlin candidate. Several days later, election authorities canceled the results of the elections and called a new vote.