Russian Prime Minister Vladimir Putin on Thursday accused the U.S. special forces of being involved in the killing of deposed Libyan dictator Moammar Gadhafi.

"Who did this?" Putin said in his annual televised phone-in with Russians.

U.S. lawmakers rebuked Moscow's leadership Wednesday for "manipulating" recent elections, and urged legislation to blacklist any Russian believed responsible for rights violations from traveling to the United States.

At a U.S. Senate hearing focused on corruption and rule of law in Russia, days after tens of thousands of demonstrators marched charging electoral fraud, State Department officials said they recognized a "national awakening" among Russian citizens calling for accountability of their government.

A leading ally of Vladimir Putin said on Wednesday he was quitting his post as Russian parliament speaker, after polls that saw the ruling party lose support and face protests against vote-rigging.

"I have decided to renounce my mandate as a member of parliament... It would be wrong to occupy the post of speaker for more than two terms," said Boris Gryzlov in a statement on the website of the ruling United Russia party.

Russian Prime Minister Vladimir Putin's spokesman said Monday the results of contested parliamentary polls will stand despite massive street protests and a probe by the election authorities.

"Even if you add up all this so-called evidence, it accounts for just over 0.5 percent of the total number of votes," Putin's spokesman Dmitry Peskov told Agence France Presse in a telephone interview.

Up to 50,000 people turned out in Moscow on Saturday for a protest against disputed polls that have sparked a rare national show of defiance against Vladimir Putin's 12-year rule.

Hundreds of security trucks blocked off central squares while helicopters patrolled the skies as Moscow authorities deployed more than 50,000 riot police and troops on the biggest day of protest to hit Russia since the turbulent 1990s.

Prime Minister Vladimir Putin, whose party lost support in parliamentary elections, Thursday named a top Russian film director to head his campaign to return to the Kremlin in March presidential polls.

Stanislav Govorukhin, who directed the classic Soviet television series "The Meeting Place Cannot be Changed,” will mastermind Putin's bid to reclaim the presidency in the elections on March 4, 2012.

Prime Minister Vladimir Putin on Thursday accused the United States of stirring up controversy over Russia's polls and warned those protesting the result they would be punished if they broke the law.

After three days of protests against election results the opposition says were rigged, Putin said the authorities should enter into dialogue with the opposition. But he accused some of its leaders of acting selfishly.

The Kremlin reacted furiously on Wednesday after an obscene posting mocking liberal blogger Alexei Navalny, who was jailed in this week's protests, reappeared on President Dmitry Medvedev's Twitter feed.

"Last night an inappropriate retweet appeared on Dmitry Medvedev's Twitter account," the Kremlin said in a curt statement.

Russian state-run television news channels on Wednesday turned a blind eye to the post-election protests in Moscow and other cities, leaving Internet sites as the only source of blow-by-blow coverage.

On Tuesday evening, as police arrested at least 300 people in a central Moscow square, the country's main news show turned to Angelina Jolie's directorial debut and a Russian woman arrested abroad for faking a $100 bill.

Russia has sent interior ministry troops to Moscow and increased the alert level of security forces after a protest of thousands of people opposing Vladimir Putin, officials said on Tuesday.

"They (the troops) have just one aim -- to ensure the security of the citizens," interior ministry forces spokesman Colonel Vasily Panchenkov told the Interfax news agency while a police spokesman said the security forces were now on a "heightened regime" of alert.