Prime Minister Vladimir Putin has accused the United States of encouraging protests over Russia's parliamentary election and said hundreds of millions of dollars in foreign funds were used to influence the vote.
In his first public remarks about demonstrations by protesters alleging Sunday's vote was fraudulent and unfair,
Putin said US Secretary of State Hillary Clinton "gave a signal" to Kremlin opponents.
"She set the tone for some opposition activists, gave them a signal, they heard this signal and started active work," Putin said on Thursday.
Putin's United Russia party won the elections but lost a significant share of its seats in the polls.
Thousands have taken to the streets since Monday and authorities say about 900 people have been arrested.
Putin said the authorities should enter into dialogue with the opposition, but said some of the protesters were pursuing selfish political aims and that most Russians do not want political upheaval.
"We are all adults here and we understand that some ... of the organisers act in accordance with a well-known scenario and in their own mercenary political interests," he said.
The US has expressed serious concern about the conduct of the elections, which Clinton suggested were not free or fair.
Opposition parties and international observers said the vote was marred by vote-rigging, including alleged ballot-box stuffing and false voter rolls.
Online protest call
The opposition has called for a mass protest to be held on Saturday in Revolution Square, just metres from the Kremlin walls in Moscow.
As of Thursday morning, more than 20,000 people had added themselves to a Facebook page calling on Russians to attend the rally.
While the gathering is officially sanctioned by the authorities, the permission is for a maximum of 300 people, raising the prospect that it will be broken up by anti-riot police if greater numbers show up.
"They have said 300. If more come then we will bring the organisers to responsibility," Moscow's deputy mayor Alexander Gorbenko told Moscow Echo radio.
But Boris Nemtsov, an ex-cabinet minister and leading opposition figure, said the gathering had to go ahead.
"The authorities are trying to intimidate their own people and doing everything that the meeting does not take place." he said.
At least 51,500 police officers and 2,000 paramilitary troops have been deployed in Moscow since the election, authorities say
About 300 people were arrested in the first night of protests and more than 550 people in the second protest a night later.
Dozens were also detained after smaller protests in Moscow and St. Petersburg on Wednesday.
Leading opposition figures, including the blogger Alexei Navalny, have already been handed 15-day jail terms. The Kommersant daily said it was unclear how many of those detained were still being held but it appeared that dozens of similar sentences had been handed out.
Rights groups have criticised the arrests of protesters, with Amnesty International saying "the scale of arrests has not been in any way justified".
"We fear that the Russian police are simply quashing opposition protest, no matter how peaceful," the group said in a statement.
On Wednesday, Mikhail Gorbachev, the Soviet Union's last leader, called on Russian authorities to annul the results of the elections.
Gorbachev told the Interfax news agency that authorities must hold a fresh election or deal with a rising tide of discontent.
"More and more people are starting to believe that the election results are not fair," he said. "I believe that ignoring public opinion discredits the authorities and destabilises the situation."
Putin, meanwhile, officially registered on Wednesday to run for the presidency in March, a position he previously held between 2000 and 2008 before being obliged to step down by the country's two consecutive terms limit.