An opposition supporter gestures as he blocks a police van transporting detained anti-corruption campaigner and opposition figure Alexei Navalny during a rally in Moscow, Russia, March 26, 2017.
The rallies are the largest to be held Russia-wide since a wave of street actions protesting against Putin's reelection to a third Kremlin term in 2011-12.
Thousands protested in more than 180 cities across Russian Federation, according to Navalny's campaign headquarters, making it the most widespread protest in the country since Vladimir Putin returned to the presidency in 2012.
The Kremlin has dismissed Navalny's graft allegations, accusing him of irresponsibly trying to whip up unrest.
Riot police detained more than 1,000 demonstrators who were out protesting across Russian Federation. "People are not afraid". In Moscow, more than 150 were detained in the city's downtown "for violating public order", says state-run Tass media.
"We were right, it was a provocation to one hundred percent of inadequate people who cannot answer their actions and words" commented head of the Moscow Security Department, Vladimir Chernikov. Reuters witnesses saw a police vehicle leaving his apartment compound at high speed, followed a few minutes later by a minibus carrying about 10 policemen.
Navalny's spokeswoman Kira Yarmish, said power at their office had been cut by authorities.
Navalny - who set it all in motion - was whisked through his court hearing on Monday and handed a 30 day prison sentence. He confirmed the sentence on his Twitter account, writing that his incarceration will force him to miss a Moscow concert in July by British band Depeche Mode.
A BBC correspondent who was among demonstrators in central Moscow said police were "pulling people out at random" and detaining them.
Roman, a 19-year-old student, said Navalny's campaign against official corruption had struck a chord. "That was when they grabbed me", he said.
"These are 16-17 year old guys, and young women who basically need to understand what prospects await them in their lives and this is a very serious thing". Medvedev, a close Putin ally, flatly denies wrongdoing.
"I wouldn't talk of a movement I think it's a preparation stage since society is getting more political", says Alexei Makarkin of the Center for Political Technologies.
The Kremlin has long felt Putin dissenters were fewer in number.
Anti-corruption demonstrations took place Monday in scores of cities throughout Russian Federation.
She spent five hours in detention and faces up to 15 days in jail for taking part in an illegal rally.
Not only did Spicer note protesters, but he mentioned the arrests of journalists as well. At the same time as the event, at the central Tverskaya Street was the final of a historic reconstruction festival.
For now, polls suggest Navalny has scant chance of unseating Putin, who enjoys high ratings.
Jill Dougherty, a Russian Federation expert and former CNNMoscow bureau chief, said Navalny was likely to be plotting his next demonstration in the lead up to the presidential election next year.
"Russia is an authoritarian regime, and I want to change it into a Democracy", he told CBS News.
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