Russian police detained more than 1,000 people in central Moscow on Saturday during a protest, the biggest crackdowns of recent times against an increasingly defiant opposition decrying President Vladimir Putin's tight grip on power.
The protesters were demanding that opposition candidates be allowed to take part in city council elections.
At least one woman and a man appeared to have suffered serious head wounds.
Thousands of protesters were expected at the unauthorised rally but opposition figures said Russian authorities had tried to intimidate them in the hope of getting the demonstration scrapped.
Police also raided an internet television station as it was broadcasting the protest.
Authorities said around 3,500 protesters took part in the demonstration.
They said Moscow local election candidates were prohibited from running because they had failed to collect a sufficient number of genuine signatures in their support, an allegation the opposition rejects as false.
Members of the opposition had their homes searched earlier in the week and leading Kremlin critic Alexei Navalny was jailed on Wednesday for 30 days for calling on people to protest.
Several opposition members were detained, including Ilya Yashin, Dmitry Gudkov and top Navalny associate Ivan Zhdanov.
Police presence was heavy at the mayor's office on Tverskaya Street, one of Moscow's main thoroughfares, with police trucks and buses parked in the building's courtyard and other buses positioned nearby to take detainees away.
"Investigators raided my home, withdrew my computers and telephone. They want to prevent us from taking to the streets," Dmitry Gudkov told Euronews on the eve of the rally.
"We want to participate in political life and elections. We want to be in the legal field but they have rejected us from that. If we're not in the election race, we are in the streets," Gudkov said as he stood outside the Russian Investigative Committee where he said he was summoned for interrogation.
Gudkov was arrested shortly before the protest.
The popularity of candidates backed by the Kremlin has been falling and opposition figures are confident of gaining support in the capital.
But many of them have been allegedly barred from contesting the elections on the grounds they haven't got enough signatures of support.
The decision by electoral authorities to bar some opposition candidates for allegedly insufficient signatures on nominating petitions has already sparked several days of demonstrations this month.
The Moscow city council, which has 45 seats, is responsible for a very large municipal budget and is now controlled by the pro-Kremlin United Russia party.
All of its seats, which have a five-year-term, are up for election on September 8.
Opposition leaders have urged people to show up saying this is not just a local Moscow issue but is a reflection of the political scene all over Russia.
"Get out on the streets, leave your comfortable sofa because your sofa is your coffin," added Gudkov.