A top ally to beleaguered Russian Prime Minister Vladimir Putin has resigned in what is likely a modest concession by the Kremlin to the rising wave of opposition against the Moscow government.

Boris Gryzlov, the 60-year-old speaker of the Duma, the lower house of Parliament, has quit -- a relatively quick response by the Kremlin to the huge (and quite unprecedented) anti-Putin protest in Moscow last weekend as well as to the startling drop in popularity of the ruling United Russia Party.

In the December 4 election, United Russia won only 238 of the 450 seats in parliament -- its worst showing ever, resulting in the loss of its former two-thirds majority

According to reports, Gryzlov was regarded as being exceptionally loyal to Putin and reportedly made sure that Parliament rubber-stamped the ruling party’s policies. He once notoriously declared that parliament was not a place for debate.

Analysts believe Gryzlov is simply being used as a sacrificial lamb (although the former speaker claimed he stepped down on his own accord).

After eight years as speaker, Gryzlov said he didn’t think he should hold the post for more than two terms.

However, Gryzlov added that he will not resign from his position as chief of United Russia Party’s Supreme Council.

Gleb Pavlovsky, a political analyst, told the Daily Telegraph newspaper: He [Gryzlov] has long been a problem for the United Russia party. In some respects he can be considered the co-author of the December 4 [parliamentary election] defeat.

Another Russian analyst, Alexei Makarkin, told the Interfax news agency: Gryzlov was serving as speaker when the situation was comfortable and predictable and when the United Russia [Party] had a constitutional majority. [But] the situation is more complex now. The new speaker must be able to conduct a dialogue with the opposition.

The Moscow Times speculated that Gryzlov will likely be replaced by either Kremlin chief of staff Sergei Naryshkin or Deputy Prime Minister Alexander Zhukov.

Meanwhile, President Dmitry Medvedev has promised he will investigate claims by the opposition that United Russia has engaged in voter fraud to rig elections.

However, Putin reportedly hasn’t changed his plans to again becoming President in elections to be held next March. He is expected to address the nation in a television broadcast on Thursday in which he will discuss the protests from last weekend as well as the recently disputed parliamentary elections.