Russian opposition leader Alexei Navalny was jailed for 15 days after the largest anti-government demonstrations for at least five years energized President Vladimir Putin's critics as presidential elections loom.

Navalny was imprisoned by a Moscow court on Monday after being convicted of disobeying police and fined 20,000 rubles ($352) for organizing an unsanctioned protest after more than 1,000 people were detained in a wave of demonstrations in cities across Russia on Sunday. Despite draconian laws forbidding unsanctioned rallies, at least 60,000 took part in more than 80 protests, according to the independent Ekho Moskvy radio station.

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"You can't detain tens of thousands of people — yesterday we saw the authorities can only go so far," Navalny told reporters in the court, where he appeared after being held overnight. "As long as people see tens of billions of dollars being stolen by top officials," they'll be ready to protest, he said.

The protests were the largest since demonstrations erupted in winter 2011 and spring 2012 against alleged vote-rigging in parliamentary elections and Putin's return to the presidency for a third term. Putin, 64, is likely to seek a further six years as president in elections next March, though he hasn't officially said he'll run. Navalny, 40, has said he'll be a candidate, but the Kremlin insists he's ineligible because of a fraud conviction that the opposition activist has dismissed as politically motivated.

'Just The Start'

"This is just the start, and the culmination will be nearer to the presidential elections," Vladimir Milov, one of the opposition leaders, said in a blog posting Monday. "Now our task is to force them into concessions."

The protests were a "provocation" and police acted "absolutely correctly, professionally and legally" in dealing with them, Kremlin spokesman Dmitry Peskov told reporters on a conference call Monday. Organizers got people to join the demonstrations on the "lie" that they'd been approved by the authorities, he said.

Navalny called the protests after releasing a film online that accused Prime Minister Dmitry Medvedev of amassing lavish properties with the help of multibillion-dollar funds. The government, which is struggling to revive the economy after the longest recession in two decades plunged millions of Russians into poverty, has denied the allegations.

QuickTake Vladimir Putin

Navalny urged the judge at his hearing to call Medvedev for questioning as the "main organizer of the protests" triggered by the allegations, according to his Twitter account. The court rejected his request.

'Serious Success'

The U.S. and the European Union condemned Russia for breaking up the protests and called for the release of those arrested.

Protesters defied the authorities' refusal to authorize the rallies. Russian news agencies reported detentions of participants in Vladivostok in the far east, as well as in cities in Siberia and central Russia. In St. Petersburg, organizers said more than 10,000 participated and at least 130 were detained.

Putin's opponents scored "a serious success" by staging the protests, which drew in young crowds in major cities, said Sergei Markov, a political analyst who acts as a consultant to the Kremlin. "This means that the new phase of the radical opposition will focus not on the elections themselves but on mass street unrest," he said on Facebook.

Still, given the "dominant grip" of Putin over the domestic political scene, "it's hard to imagine the latest demonstrations being allowed to get out of control to the point of threatening the regime itself," Tim Ash, senior strategist at Bluebay Asset Management, said in an emailed note.

Police raided Navalny's Anti-Corruption Fund as it carried live internet broadcasts of the demonstrations, detaining staff on suspicion of extremism and confiscating all the computers, according to the fund. Video of the protests placed online by his supporters had received 3.8 million views by Monday.

'Bolder' Protesters

The authorities are uncertain over how to respond to the resurgent opposition — either through a full crackdown using laws passed after the last wave of rallies that allow them to fine and jail protesters, or by trying to appease critics with steps to make the presidential elections more open, said Igor Bunin, the head of the Moscow-based Center for Political Technologies.

"Probably they will stick to a middle path," Bunin said by phone. "For now, Putin isn't personally at risk but we don't know how far public consciousness will develop as it's clear that dissatisfaction will increase."

Unlike the 2011-2012 protests, which involved mainly middle-class Russians, the new opposition movement is driven by a young generation that "has its whole life ahead so it's going to be much more determined and bolder," Bunin said.