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Mikhail Metzel, Associated Press
Alexei Navalny, a prominent anti-corruption whistle blower and blogger, speaks to journalists after being released from a police custody on the outskirts of Moscow early Wednesday, Dec. 21, 2011. Navalny was detained on Monday, Dec. 5, along with some 300 protesters who rallied against what they called vote rigging during Sunday's parliamentary election.

MOSCOW — Two leaders of Russia's political opposition were released Wednesday from the Moscow jail where they were held for 15 days for their roles in a protest that set off a wave of protests across the country.

Alexei Navalny, a corruption-fighting lawyer and prominent blogger, and Ilya Yashin were arrested the day after the Dec. 4 parliamentary election while leading a protest against vote fraud that allegedly boosted the results for Vladimir Putin's party.

The Dec. 5 protest unexpectedly drew more than 5,000 people, the biggest opposition rally in years, and helped to energize Russians discontented with Putin's rule. A protest five days later drew tens of thousands in Moscow, while demonstrations attracting from a few hundred to 1,000 people took place in more than 60 other cities.

Navalny told supporters who waited for his release in the pre-dawn darkness that he "was jailed in one country and freed in another."

Another nationwide protest is being held Saturday. Navalny, a charismatic speaker, is expected to address the crowd.

Putin, now prime minister, had been counting on a strong showing for his United Russia party in the election, both to maintain his control over parliament and to add legitimacy to his plans to return to the presidency through an election in March.

United Russia, however, had come to be seen as serving the interests of a corrupt bureaucracy and was widely known as "the party of crooks and thieves," a name originally coined by Navalny.

Putin remains more popular than his party, although the protest movement is now posing the strongest challenge to his rule since he first came to power in early 2000.

Navalny said the focus now should be on demanding a free and fair presidential election through peaceful national protests.

"For Putin to leave, we don't have to loot stores and set them on fire," he told supporters in a video posted on the site of Ekho Moskvy radio. "People need to come out and express their will and show that they themselves are the power."