On Saturday, Russian police violently clashed with protesters in Moscow and arrested more than 1,800 demonstrators in cities across the country as Russians took to the streets to denounce Kremlin rule and demanded the release of opposition leader Alexei Navalny.

Tens of thousands demonstrated across Russia after Navalny called on his supporters to take to the streets this week following his detention in a Moscow airport upon his arrival from Germany, where he had been recovering from a near-fatal poisoning with the Novichok nerve agent.

Protesters flooded Pushkin Square in central Moscow and nearby streets, attacking heavily armed riot police with snowballs but were detained in large numbers and beaten back by law enforcement wielding batons.

At one point, protesters massed on the steps of Moscow's circus, illuminating the crowds with hundreds of cell phone lights and throwing snowballs at a police van.

"Criminals dressed in uniforms are protecting criminals at the helm," Vera Spivakova, a 71-year-old pensioner, told.

"Putin and the oligarchs are afraid of losing their trough," she added.

OVD Info, which monitors opposition rallies, said that more than 1,800 were detained in dozen of cities.

Among more than 300 detained in the capital were Navalny's wife Yulia Navalnaya -- who was later released and prominent activist Lyubov Sobol. Several Navalny associates were fined and jailed on the eve of the protest.

"What a joy that you are here!" Yulia Navalnaya posted on Instagram before being bundled off into a police van.

The Investigative Committee, which probes major crimes, said in a statement it launched several precursory probes into violence against law enforcement.