Russian opposition leader Alexei Navalny has been sentenced to 15 days in jail for his role during mass demonstrations.
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.
It was the biggest show of defiance since anti-government protests in 2011.
Journalists and well-wishers on Monday packed the courtroom in central Moscow where Navalny was taken.
Since then, he has used his social-media influence to rally critics of the Russian government, and recently declared his intention to run in the 2018 presidential race - despite a criminal conviction in February on fraud charges that made him ineligible to compete in the election but was widely viewed as a political ploy to keep him out of the race.
Complaining about the judge striking down one motion after another, Navalny told reporters: "Even the slightest illusion of fair justice is absent here".
Reacting to his sentence, the vocal critic of President Vladimir Putin said: "I think yesterday's events have shown that there are quite a large number of voters in Russian Federation who support the programme of a candidate who speaks for the fight against corruption".
The Kremlin has long sought to cast the opposition as a phenomenon of a privileged Westernized urban elite out of sync with broader layers of the population in Russia's far-flung regions.
Meanwhile, the US State Department "strongly condemned" the detention of hundreds of protesters throughout Russian Federation, including of Navalny.
Putin's spokesman chided the organizers for inciting illegal acts.
"The Kremlin respects the civil position of the people and their right to express this position..."
"We can not respect those who deliberately misled underage minors promising them some payment in return for participating in an unauthorized protest, thereby exposing them to danger", Peskov said, according to state-run news agency Tass.
Mr Peskov defended the Russian police in riot gear who were seen manhandling protesters, some of whom were minors, calling their response "highly professional and lawful".
Peskov claimed the Kremlin was "sober about the scale of yesterday's protests, and ... not inclined to diminish them or push them out of proportion".
The unsanctioned protests were the biggest public gatherings since the 2011/2012 anti-Kremlin demonstrations.
Mr Putin "constantly talks to people" and is well-briefed on the sentiment in the country, Mr Peskov insisted.
The United States and the European Union voiced deep concern about the detentions, with the State Department describing them as an "affront to democracy".
Over the years, Navalny, a lawyer, has evolved from a lone blogger to someone who leads a group of like-minded activists, the Anti-Corruption Foundation.
On Sunday, Russian opposition figure Alexey Navalny organized an anti-corruption rally without the permission of Moscow authorities in the Russian capital, which was attended by some 8,000 people with some 600 people, including Navalny himself, being detained by police. He spent the night in the police station before being brought to the court.
Navalny was among those detained and is now facing charges of organizing an illegal rally.
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The Washington Post reported that two people suffered minor injuries; however, they did not require medical attention. KCBS reports that one person was pepper-sprayed by a demonstrator and another was punched.
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