Russian Prime Minister Vladimir Putin has rejected calls to re-run disputed parliamentary elections but said he accepted "lawful" protests.
In a televised live chat, he proposed installing web cameras at polling stations to prevent fraud at the March presidential poll where he is standing.
But he insisted the parliamentary results were valid and was scathing about some protesters.
Opposition supporters appeared unmoved by Mr Putin's comments.
Mr Putin also strongly attacked US foreign policy, and sought to dismiss warnings of his own downfall after more than a decade dominating Russian politics.
After serving two terms as president from 2000 to 2008, Mr Putin was obliged under the Russian constitution to step aside after his second term but is now entitled to stand again.
"The fact that people express their opinion... is an absolutely normal thing as long, of course, as everybody acts within the framework of the law," he said, after protests on Saturday which saw around 50,000 people turn out in Moscow alone.
"If this is the result of the Putin regime I am quite happy and quite content with that. I don't see anything wrong with it," he added.
Thursday is the deadline for would-be independent presidential candidates to declare their bids, which must satisfy rigorous criteria at the central electoral commission (political parties have until Tuesday to submit their candidates).
Established opposition party leaders Vladimir Zhirinovsky, Gennady Zyuganov, Sergei Mironov and Grigory Yavlinsky are all expected to stand, as is billionaire Mikhail Prokhorov.
One surprise candidacy is that of Putin ally Dmitry Mezentsev, who is governor of the Irkutsk region of eastern Siberia, and other names include radical opposition figure Eduard Limonov.
In another development on Thursday, senior Kremlin strategist Vladislav Surkov was promoted to acting head of the presidential staff, where he was hitherto deputy head.
'Webcams everywhere'
Instances of ballot-stuffing were identified widely by Russian activists using social media to report them.
Concern over the conduct of the December parliamentary elections was expressed by foreign observers from the OSCE and others.
After meeting Russian President Dmitry Medvedev in Brussels on Thursday, European Council President Herman Van Rompuy voiced concern at the reported "irregularities and lack of fairness" as well as the detention of protesters.
Speaking at the same news conference, Mr Medvedev refused to comment on a call by the European Parliament for an "immediate and full investigation" into allegations of poll fraud, saying the parliament had "nothing to do with" Russia's elections.
Mr Putin said: "As regards vote-rigging and the fact that the opposition are not pleased with the election results, there is nothing new here, this has always been the case.
"The opposition is there to fight for power and is fighting for power. That is why it is seeking any opportunity to come closer to power, to edge the current authorities out, to accuse them, to point to their mistakes."
Mr Putin appeared to mock some opposition protesters, likening their white ribbon symbol to a condom.
"I decided that it was an anti-Aids campaign... that they had, excuse me, pinned on contraceptives, only folding them in a strange way," he said.
Without naming any foreign powers, he condemned "coloured revolutions" such as the Orange movement in Ukraine as a "tested and tried scheme to destabilise society".
He said he was asking Russia's central electoral commission to install web cameras at all polling stations, saying he believed there were more than 90,000 of them.
"Let them operate round the clock, night and day, transmitting everything to the internet, so that the country sees what is happening at a specific ballot box, to remove any falsifications altogether," Mr Putin said.
'Cynical spectacle'
Mr Putin laughed off a Russian press row over a photo of a spoilt ballot-paper on which was scrawled an obscene message addressed to himself.
Referring to the report in Kommersant Vlast magazine, which led to the sacking of two top executives by its owner, he said: "The ballot-paper was photographed in London and you and I know who lives in London.
"Their wish to tell me to go you know where is linked to the fact that they want to come back here themselves and, while I'm here, they can't come back."
It was not clear whom Mr Putin was referring to, but the UK is frequently accused by Moscow of harbouring fugitives from justice in Russia.
One Moscow tweeter, going by the name Aafinogen, claimed that during Mr Putin's speech, the number of people signing up to a Facebook page for a protest rally in the city on 24 December had risen by 3,500 to 21,500.
Liberal opposition figure Boris Nemtsov said Mr Putin's live show had been carefully planned in order to present him in the best light.
"Everybody knows that this is not a real reality show," he said.
"Everybody knows that everything was prepared: questions and answers, all of them. They prepare and it looks like a cynical spectacle to show that he's still strong, he's still popular, he knows how to run the country in the future."
McCain 'nuts'
The Russian prime minister dismissed a warning by former US presidential candidate and Vietnam veteran Senator John McCain that he faced being overthrown like Muammar Gaddafi in Libya.
"McCain was captured during the war and kept in a pit - it would drive anyone nuts," Mr Putin said.
Sen McCain tweeted in response: "Dear Vlad, is it something I said?" before retweeting his statement on Russia from last week in which he talks of the "growing frustration that Russians feel for their rulers".
On US foreign policy, the Russian leader said: "America doesn't need allies, it needs vassals."
"Did anyone in the States consult their allies about what to do in Afghanistan?" he asked rhetorically. "Damn right they didn't!"
Russia, by contrast, had "more friends than foes" abroad despite attempts to "shunt" it aside, Mr Putin said.
Warning against perceived threats to Russia, he paraphrased a famous saying by Tsar Alexander III, saying: "They all fear our hugeness."
US indignation
Mr Putin suggested the US military had organised Gaddafi's death.
"Who killed Gaddafi?" Putin asked. "Drones! American ones! They struck his convoy. And then by radio, via special forces that should not have been there anyway, they brought in so-called oppositionists and fighters and killed him without trial or investigation."
Washington responded by saying the suggestion that US special operations forces had been involved was "ludicrous".
"We did not have American boots on the ground in the Libya operation," US Defence Secretary Leon Panetta's spokesman, Captain John Kirby, told AFP news agency.
"All our support was done through the air and on the seas."
In other points Mr Putin
Asked to explain why spectators had booed when he entered the ring at a martial arts contest in Moscow last month, Mr Putin said: "Maybe the sight of my face in the ring didn't please somebody? I quite accept that.
"Maybe they were unhappy with [defeated fighter] Jeff Monson? Maybe they were unhappy with the fight? Maybe they thought it had been rigged!"
Asked for his views on the internet, the medium favoured by opposition activists, Mr Putin said: "Shutting the internet is technologically difficult and wrong politically."
Over four hours and 33 minutes of live broadcasting, the Russian prime minister was also asked about his personal life. Asked what made him happy, he said: "I find my happiness in love."
