Russia has jailed the Kremlin's most prominent critic for 15 days

Prominent Russian opposition leader Alexei Navalny has been jailed for 15 days for disobeying police orders during huge anti-government protests Sunday.

Navalny, a 40-year-old lawyer and activist who plans to run for president in 2018, was the organizer of protests across the country that called for the resignation of Russian Prime Minister Dmitry Medvedev over corruption allegations. The mostly unsanctioned protests, held in more than 80 towns and cities from St. Petersburg to Vladivostok, were the largest in Russia since a wave of street rallies in 2011 and 2012 over alleged electoral fraud, and were notable for the young age of the protesters. Russian newspaper Kommersant reported that about half were students.

Navalny was sentenced Monday, by the same court that fined him 20,000 rubles ($350) for organizing the protests earlier in the day.

During the hearing, Navalny was in a combative mood, asking the court to call Medvedev as a witness to account for why so many people had turned out to protest, and at one point compared the judge to his 15-year-old daughter. “When she is wrong she, like you, also becomes rude,” reporters in the courtroom quoted him as saying.

Ahead of the sentencing, Navalny posted a selfie to his Twitter account saying: “The time will come when we will judge them (but fairly).”

Navalny, who has built his political profile by railing against government corruption on his blog, was behind a report released earlier this month alleging that Medvedev had taken more than $1 billion in bribes. The Kremlin has dismissed the allegations, and on Monday rejected calls from the U.S. and E.U. to release protesters who were still being held, accusing organizers of having paid some of the crowd to attend.

Kremlin spokesman Dmitry Peskov said while the government respected protesters right to voice their position, it could not respect those “who consciously misled people and who consciously did it yesterday and provoked illegal actions.”

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.”

A Russian monitoring group, OVD-Info, said that 1,030 people had been detained at the protests in Moscow alone, with about 120 still in custody. Most of those released had been charged with taking part in an unauthorized protest. Hundreds were reportedly arrested in other cities.

Keir Giles, a director of the Conflict Studies Research Centre, told VICE News that the demonstrations, though not large in size, were remarkable in Russia’s modern political climate. He said one possible reason for the strong turnout was the arrival on the political scene of a new generation of young Russians “that thinks of things in Western liberal terms – that leadership corruption is actually something you stand up against.”

“It could be that they’re taking an entirely different view to the post-Soviet generation immediately before them, that is nostalgic for the glory days of a Soviet Union they never knew,” he said, conceding that this was “an optimistic explanation.”

Giles described Navalny as the “most popular remaining opposition leader.” “But that’s not saying much, because their popularity is measured in tiny increments compared to the current leadership,” he said.

“Post-Soviet Russia has been good at dividing any liberal democratic movements in order to make sure they don’t constitute a single opposition bloc – and of course from time to time individuals who become particularly prominent are either bought off or bumped off.”

Navalny ran for mayor of Moscow in 2013, coming in second place with about quarter of the vote behind a Kremlin appointee. He has previously been convicted and handed a suspended sentence on embezzlement charges – which were widely seen as politically motivated.