Alexei Navalny, Russia's most prominent opposition politician, has been convicted of fraud charges in Moscow, as has his brother Oleg. The charges are widely considered to be politically motivated; he has called for protests in response.

In recent years, Navalny has played a key role in organizing mass protests against President Vladimir Putin's government and policies. In 2013 he came in second in Moscow's mayoral election by running on an anti-Putin platform. The year before, the Wall Street Journal called him "the man Vladimir Putin fears most."

called him "the man Vladimir Putin fears most." Both brothers were sentenced to three and a half years in prison, fined 500,000 rubles, and ordered to pay 4 million rubles restitution. Alexei Navalny's three-and-a half-year prison sentence has been suspended, but Oleg was given a custodial sentence, and will be jailed immediately.

What comes next: protests and a "hostage"

The brothers were convicted of embezzling approximately half a million dollars from two firms, one of which was an affiliate of Yves Rocher, a French cosmetics company.

Oleg's detention was immediately denounced by anti-government protesters who accused the Kremlin of using him as a "hostage" to put pressure on Alexei. Radio Free Europe reports that Ilya Yashin, another prominent Russian opposition politician, said that "This is a mechanism of pressure on a person: try fighting corruption when your brother's in jail."

Speaking outside the courthouse after the sentencing, Alexei Navalny said that "this regime has no right to exist," and called on Russians to take to the streets in protest "until the regime which tortures innocent people is removed."

18,000 people have said they are going to a protest in Moscow's Manezh Square today to protest the Navalny verdict. It is scheduled to begin at 7 pm local time, which is 11 am EST.