Russian opposition leader gets jail sentence after mass protests Alexei Navalny got a 15-day sentence plus a fine.

 -- Russian opposition leader Alexei Navalny, who has challenged President Vladimir Putin's rule on an anti-corruption platform, appeared in a Moscow court today as the Kremlin spoke out for the first time on the mass anti-government protests Sunday that rocked the country, saying the demonstrations were based on "provocations and lies."

Navalny was fined 20,000 rubles (roughly $350) and given a 15-day jail sentence for violating public meeting rules and disobeying police.

Navalny was one of hundreds of people arrested in a crackdown after thousands protested in the nation's capital and in other cities across Russia.

Between 7,000 and 30,000 people demonstrated in Moscow, and up to 10,000 in Saint Petersburg in what were Russia's largest anti-government protests in several years.

Independent radio station Ekho Moskvy estimated that unsanctioned rallies in 82 cities and towns assembled 60,000 opposition supporters, which would make the anti-Kremlin demonstrations the largest since 2008.

Navalny tweeted out a picture of himself from the court where he was being held prior to his hearings.

"Hello everyone from Tversky Court. The time will come when we will have them on trial (but honestly)," Navalny wrote.

After staying mum about the protests and arrests Sunday, the Kremlin unleashed harsh words about the demonstrations today.

“In essence what we saw in several places, especially in Moscow — it was provocation and lies," Kremlin spokesman Dmitry Peskov said.

Peskov seemed to point a finger at organizers of the protests, saying that those "who explained in a highly subtle and academic language that it was a lawful action and didn’t contradict the law, they were speaking a pure lie.”

He also suggested that some teenage protesters had been paid to be there, saying they had received “certain rewards”.

Peskov said the Kremlin views Russian citizens’ right to express their opinion in pre-approved protests “with respect,” but that Sunday's demonstrations were illegal.

"We regret that our active citizens, many probably out of ignorance, didn’t want to use the alternative venues [offered by authorities for the protests far outside the city center],” the spokesman said.

The march was an “absolutely forbidden protest action,” and police behaved correctly in making arrests, he said.

About 500 people were arrested in Moscow, according to Interfax, a privately-held, independent Russian news agency. Russian human rights group OVD-info put the number higher, att more than 700 people detained in Moscow plus 34 in St. Petersburg and between 80 and 100 in other cities.

The State Department criticized the arrests, calling on Russia to immediately release all the demonstrators who had been detained.

"The United States strongly condemns the detention of hundreds of peaceful protesters throughout Russia on Sunday," acting spokesman Mark Toner said. "Detaining peaceful protesters, human rights observers, and journalists is an affront to core democratic values. We were troubled to hear of the arrest of opposition figure Alexei Navalny upon arrival at the demonstration, as well as the police raids on the anti-corruption organization he heads."

The European Union has also called on Russia to “release without delay” what it called peaceful protesters.

ABC News' Ben Gittleson, Patrick Reevell, Mike Trew, Anastasia Butler, Dean Schabner, JJ Gallagher, and The Associated Press contributed to this report.