UPDATED: 12:02 p.m. Eastern / 8:02 p.m. in Moscow

A massive crowd of protesters gathered in Moscow's Manezhka Square on Tuesday following the guilty verdict of anti-corruption crusader Alexei Navalny.

Navalny, a leading foe of Russian President Vladimir Putin, was found guilty of fraud and given a suspended sentence of three and a half years on Tuesday, while his brother was sent straight to prison.

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"The government isn't just trying to jail its political opponents — we're used to it; we're aware that they're doing it — but this time they're destroying and torturing the families of the people who oppose them," he said, calling for people to attend the protest on Tuesday evening.

Hours after the ruling, Navalny himself appeared alongside protesters at Moscow's Manezhka Square in defiance of a house arrest order — and was quickly detained by Russian authorities for breaking the terms. He was taken away in a bus and escorted back to his home.

Alexey Navalny escaped his house arrest and is moving towards manezhnaya square pic.twitter.com/JfGPve0kFM — Feldman (@EvgenyFeldman) December 30, 2014

Protesters chanted "Free Navalny! Free Russia!" and "Russia without Putin!" as he was carted away in a police bus.

"That they arrested me doesn't mean anything. I'm not able to do anything you aren't able to do," he wrote on Twitter, tweeting, apparently, from the police van to his supporters on the square.

Police and demonstrators began to gather there at 7 p.m. local time as the crowd slowly grew, which security officials said was unsanctioned and therefore would be stopped.

View of the #manezhka crowd in Moscow square seen from above pic.twitter.com/tacWBoNnyj (Pic: @rykov) — Mashable News (@MashableNews) December 30, 2014

Happy new year from Moscow riot police pic.twitter.com/wXByTQ9W9I — Feldman (@EvgenyFeldman) December 30, 2014

Many appeared dressed warmly for the cold night, waving flags in defiance of the police and chanting anti-Putin slogans.

Группа юношей с георг.ленточками построилась и двинулась к #Манежка pic.twitter.com/bE2vC1evrE — Jüri Maloverjan (@MaloverjanBBC) December 30, 2014

A Moscow-based independent human rights monitor reported that 171 demonstrators had been arrested as of 8:45 p.m. Moscow time. Police in riot gear were seen on a live stream grabbing protesters and pulling them towards busses, while pushing others away from the square.

moscow cops now pushing protestors off manezh square pic.twitter.com/njjuU9n5ym — Ilya Mouzykantskii (@ilyamuz) December 30, 2014

Fearing the Russian government would shut down Facebook ahead of the protest, organizers had encouraged supporters to download and use FireChat to communicate with each other.

Leonid Volkov, the event's lead planner, said more than 25,000 people had subscribed to the event on the mobile app, and over 30,000 were expected to attend.

The #FireChat room for tonight’s protest is buzzing with words of support from around Russia & early logistics. pic.twitter.com/mhOV3TAjdz — Kevin Rothrock (@KevinRothrock) December 30, 2014

The U.S. embassy in Moscow issued a security warning urging Americans to stay away from the square on Tuesday, raising concerns of a possibility of large crowds and violence.

According to the Moscow police, Navalny supporters have not applied for an official protest permit and officers have been instructed to remove protesters from Manezh Square. Police officers have already been deployed to Manezh Square in anticipation of tonight’s protest. Due to the possibility of large crowds and violence, Americans should avoid Manezh Square and the surrounding area including metro stations for the remainder of the day.

Ultimately, though, the demonstration was limited to no more than a few thousand supporters, and was broken up by Moscow police by 9:30 p.m. local time.

This story is developing... Additional reporting by The Associated Press.