Russian police have arrested hundreds of people and broken up protests in Moscow and St Petersburg following Vladimir Putin's victory in the presidential election.
Police moved in to disperse a protest at Pushkin Square in central Moscow, after hundreds of people refused to leave the venue at the end of a larger rally earlier.
Activists who installed themselves on top of a fountain in the square were pulled off it and dragged away.
Riot police cleared the square, moving away even bystanders that had not been at the rally. "Power to millions, not to the police!" and "Russia without Putin!" people shouted.
Moscow police also arrested dozens of protesters at a separate unsanctioned event near the central election commission, including the leader of the Other Russia radical opposition group Eduard Limonov.
The Interfax news agency quoted a police source as saying that around 150 people were detained at the actions in Moscow, but comments posted on social networks by activists suggested the final figure could be even higher.
Ilya Ponomaryev, one of the few deputies in the Russian parliament to support the protest movement, told Interfax that as many as 1,000 people could have been arrested in the city.
Police in Russia's second city of St Petersburg also broke up an unsanctioned opposition protest, detaining hundreds of people.
Election result 'unfair' - monitors
Earlier today, international vote monitors said the presidential election was unfair and clearly skewed in favour of Mr Putin.
The monitors said Mr Putin was given a clear advantage over his rivals in the media and that state resources were used at a regional level to support his bid for a third presidential term.
The observers, from the Organisation for Security and Co-Operation in Europe and the Council of Europe's Parliamentary Assembly, also called for alleged electoral violations to be thoroughly investigated.
Mr Putin last night told tens of thousands of supporters at the Kremlin that he had won in "an open and honest battle".
Russian opposition groups have reported widespread fraud. Mr Putin's opponents said they do not recognise the results and will rally near the Kremlin.
His nearest rival, Communist Party leader Gennady Zyuganov, won about 17% of votes, and nationalist Vladimir Zhirinovsky, former parliamentary speaker Sergei Mironov and billionaire Mikhail Prokhorov polled below 10%.
Mr Zyuganov said his party would not recognise the result and called the election "illegitimate, dishonest and not transparent". Liberal leader Vladimir Ryzhkov also said it was not legitimate.
Despite the opposition, mainly among well-educated and relatively well-off young professionals, Mr Putin's support remains high in the provinces and his victory had not been in doubt.
The initial challenge for the man credited by many Russians with rebuilding the country's image and overseeing an economic boom in his first presidency had been to win more than half the votes and avoid a second-round run-off.
His clear victory will enable him to portray his return to the presidency as a strong sign of public support against the protesters, whom he has portrayed as a destabilising minority and pawns of foreign governments.
But the mood has shifted in the country of 143m and the urban protest movement portrays him as an obstacle to change and the guardian of a corrupt system of power.
After four years as prime minister, the former KGB spy now returns to the post he held from 2000 until 2008.
"I promised you we would win. We have won. Glory to Russia," Mr Putin, who was flanked by outgoing President Dmitry Medvedev, told tens of thousands of flag-waving supporters last night under the Kremlin's red walls.
Mr Putin, 59, is on a collision course with the mainly middle-class protesters who have staged rallies in the capital and other big cities since a disputed parliamentary poll on 4 December.
The protest organisers, who see Mr Putin as an autocratic leader whose return to power will stymie hope of economic and political reforms, said their demonstrations would now grow.
"He is forcing things to breaking point. He is declaring war on us. As a result the base of aversion to him is growing," said journalist Sergei Parkhomenko, one of the leaders of the opposition protest movement.
Elsewhere, EU foreign affairs chief Catherine Ashton has urged Russia to address "shortcomings" in the vote to return Mr Putin to the Kremlin in the European Union's initial reaction to the poll.
Ms Ashton's spokeswoman Maja Kocijancic told a news briefing, that the office shared concerns expressed by international observers led by the OSCE.