Hundreds of people have been arrested in Moscow as a mass demonstration against Vladimir Putin on the eve of his inauguration as president turned violent.
Eyewitnesses reported seeing hundreds arrested during bloody clashes in the streets as riot police clubbed demonstrators.
But a small group of radical protesters who hurled bottles and stones at police were also blamed for provoking the violence.
The police said on Sunday they had made 450 arrests, while 27 persons, mostly police officers, were injured.
Estimates on the turnout varied, but suggested tens of thousands took part in this year's biggest anti-Putin rally.
The organisers said 100,000 attended. The Interior Ministry said the crowd was only 8000. Experts at the scene estimated the number at between 50,000 and 70,000.
Russian opposition leaders were among those detained by Moscow police during the clashes.
According to the Itar-Tass and the Interfax news agencies, former deputy prime minister Boris Nemzov, Left Front leader Sergei Udaltsov and blogger and lawyer Alexi Navalny were held under laws allowing up to 15 days of detention.
At least six persons were treated in city hospitals for bruises, abrasions and cuts after the clashes.
Putin spokesman Dmitry Peskov called for "troublemakers" among the demonstrators to be severely punished, the Echo Moskvy radio station reported. A senior prosecutor, Vladimir Markin, said the ringleaders would be hunted down.
Media reports said they faced up to 10 years in prison.
There was also one accidental death reported, when a man taking photos of the demonstration lost his balance and fell out of an upper window of a building.
Rights activists accused police of exerting unrestrained brutality during Sunday's protests, pointing to footage showing the anti-terror unit of the special police using clubs indiscriminately against peaceful protesters.
At least six people were admitted to hospital with bruises, abrasions and even cuts.
Previous anti-Putin protests held during the winter months had always been peaceful.
According to police, difficulties broke out when the police tried to force the demonstration into a Moscow square. A number of opposition protesters refused the order and broke through a police cordon near a movie theatre.
At one point some protesters staged a sit-in that blocked traffic, leading to violence, including the throwing of stones and bottles.
Witnesses reported that the situation escalated because police attempts to guide the crowd along the reserved march path was slow and full of obstructions.
Gennadi Gudkov of the Just Russia party blamed the resulting violence, which included an explosion, on a radicalisation of the mood among the population.
"The reason is that there is no dialogue between those in power and the people," Gudkov was quoted by the Interfax news agency as saying.
The Moscow demonstration started in the city centre led by an orange banner saying, Change Requires Solidarity, the opposition internet portal Kasparov.ru reported. Smaller protests were reported in other parts of Russia.
Pro-Putin groups were to demonstrate in his favour in the evening and asserted they would bring out 50,000 supporters.
Putin, 59, is set to take over Russia's presidency again on Monday. He previously held the office for two terms, beginning 2000 and 2004, then occupied the less powerful position of prime minister for four years.
He won a third term with 63.6 per cent of votes in a March 4 election amid accusations of fraud.
The opposition march and final rally were intended to step up pressure on Putin to introduce liberal reforms.