Russian authorities charged four men Thursday with committing hooliganism and violence against police last month during the biggest opposition protest in central Moscow for years.
The four men, Alexander Shpakov, Stanislav Zimovets, Yury Kuliy and Andrei Kosykh, all between 30 and 40 years old, had all been arrested and are in custody.
They "used violence against representatives of the authorities" during the "unsanctioned action", said a statement from Russia's Investigative Committee.
The anti-corruption rally on March 26 was called by opposition politician Alexei Navalny following his report on alleged luxury properties controlled by Prime Minister Dmitry Medvedev through shadowy foundations.
The gathering -- and other smaller ones around the country -- was the largest in years to challenge the Russian authorities and ended with around 1,000 arrests.
The committee's statement said Shpakov "hit the face of a police officer several times", Kosykh hit an officer several times, including "with his foot in the head", and Zimovets "threw a brick into a national guard officer."
"Irrefutable evidence" has been collected implicating the four, including video footage, claimed the Investigative Committee, also accusing "organisers" of the rally of misleading people into thinking it was allowed by city hall.
Earlier Thursday Russian media reported that investigators also broke into the home of opposition activist Vyacheslav Maltsev in the town of Saratov and flew him to Moscow as part of a probe into an assault on a government employee.
Maltsev last year ran for a parliament seat and keeps a popular YouTube channel with critical political commentary.
Navalny called the probe into violence against police at the rally "fabricated".
The populist politician -- who is has said he will stand for president at an election next year -- has announced another round of protests for June 12.
Russian authorities have a history of launching high-profile cases after major protests, notably the probe into violence at the May 6, 2012 rally which led to dozens of people being prosecuted, including for throwing a lemon.
Many of those targeted in the case spent several years in jail while others fled the country.