The Russian Prime Minister, Vladimir Putin, accused the U.S. of encouraging protests over the country's recent Parliamentary elections.

He said hundreds of millions of dollars in foreign funds were used to influence the vote. Putin said U.S. 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, said Putin.

In an election marred by complaints of violations, including ballot-stuffing, the ruling United Russia party lost 12 million votes, or more than a quarter of the support it garnered four years ago. Thousands of people took to Moscow streets in the two days after the vote to protest the results.

The anti-government protest movements have gathered momentum, as tens of thousands of people said they were prepared to take to the streets this weekend in the biggest challenge to Putin's rule.

Helicopters hovered in the skies over Moscow, while police presence on the streets of the Russian capital remained strong following two protests that led to hundreds of people being arrested.

Mikhail Gorbachev, the former premier who oversaw the end of the Soviet Union, called on the Russian authorities to annul the results and hold a new vote.

More and more people are starting to believe that the election results are not fair, he told the Interfax news agency.