Alexei Borisov was diagnosed by doctors as having a punctured lung, three fractured ribs and a broken tooth after he attended a rally on Jan. 31 in support of Russian opposition politician Alexei Navalny.
The 42-year-old truck driver said he was injured by police who detained him after he led a march in central Ryazan, 200 km (120 miles) southeast of Moscow, shouting "Freedom to Alexei Navalny" and slogans against President Vladimir Putin.
"I was lying face down on the (police car) floor... They began to hit me, I didn't even see how many of them there were," Borisov said.
Reuters did not witness the incident Borisov described but he provided medical documents that confirmed his injuries and a photograph showing him lying in hospital. The documents did not show where or how he sustained the injuries.
Asked about his case by Reuters, the interior ministry, which is in charge of the police, did not comment.
Borisov is one of more than 11,000 people who have been detained at protests in recent weeks over Navalny's arrest and imprisonment, according to OVD-Info, a non-governmental group that monitors arrests during mass protests and seeks to prevent human rights abuses and political persecution.
An OVD-info representative said the group knew of about 116 cases of alleged police violence following the recent protests and feared many more had not reported their injuries.
Reuters has been unable to determine how widespread complaints of police brutality have been at protests that have involved tens of thousands of people in the last few weeks.
The vast majority of protesters have not complained of being hurt and no deaths have been reported. But reporters say police have been much more forceful, and in some cases more violent, than at most other political protests in recent years.
The interior ministry, the Investigative Committee which investigates major crimes and Russia's National Guard did not respond to requests for comment about the police conduct.
The Kremlin has denied repression by the police. It has said any cases of alleged police brutality are being looked into but that there have been many more cases of riot police officers being attacked by protesters than vice versa.
The authorities have called the protests illegal because they have not received official approval to go ahead, and said such rallies risk spreading COVID-19.
TASERS AND BATONS
Navalny was arrested in January after returning to Russia from Germany, where he was treated after being poisoned in Siberia with what many Western countries said was a nerve agent. Navalny blamed Putin for the attack but the Kremlin has dismissed the accusations and questions whether he was poisoned.
Reuters reporters in Moscow and St Petersburg have seen protesters tasered and beaten with truncheons, and have spoken with eight who say police used violence against them.
A Reuters reporter in Moscow witnessed a protester falling to the ground and screaming in pain during his arrest at a protest on Jan. 31, and asking the police to stop tasering him.
After a week in jail, the same protester, 30-year-old fitness trainer Soso Glonti, told Reuters a policeman had tasered him even though he was not resisting arrest.
"I know how to endure (pain), but the fifth or sixth time they tasered me I lost my temper. It was the fifth time when I started screaming," he said.
Medical records of four protesters viewed by Reuters detailed injuries including a broken arm, concussion, a head injury, bruises, and an eyelid wound.
The RIA news agency said the National Guard is looking into an incident in which an officer hit cameraman Fyodor Khudokormov, 18, who told Reuters he was beaten around the head with a baton on Feb. 2 even though he was clearly identified as a journalist.
Victor Lipatov, a 49-year-old lawyer, told Reuters he was hit on the head and arm with a baton while standing in front of riot police and holding hands with other protesters.
OVD-info group says Russia has opened 36 criminal cases against people who attended rallies over alleged use of force against riot police.
The Investigative Committee said 21 criminal cases were opened after the first rally on Jan. 23, including against protesters accused of striking policemen. It has not said how many have been opened since then.
The Investigative Committee says it has opened criminal cases against protesters who threw fireworks or other objects at policemen, kicked or punched them, or sprayed pepper gas.
Russia's Committee Against Torture monitoring group said it had filed six complaints to the Investigative Committee over alleged use of violence by riot police but had not yet received any answers. They included Lipatov's case.
No criminal cases have been announced against police officers or National Guardsmen.