A leading ally of Russian Prime Minister Vladimir Putin has resigned as speaker of the country's parliament.

Boris Gryzlov announced his resignation Wednesday in a statement posted to the ruling United Russia party website. Gryzlov, who was elected as speaker in 2003, said he would renounce his mandate as a member of parliament, but says he will continue his post as chairman of United Russia.

The former speaker did not mention the controversy surrounding the December 4 parliamentary elections, which saw United Russia lose support with a reduced majority in the State Duma. Reports of widespread fraud led to anti-government demonstrations across the country.

Leaders of United Russia — which has dominated Russian politics for more than a decade — have denied cheating.

The Communists, along with the nationalist Liberal Democrats and Just Russia — a social democratic party — all made strong gains in the vote, meaning United Russia will be forced to work with the newly empowered opposition.

If Mr. Putin regains the presidency, the 59-year-old leader could serve two more six-year terms and remain in power until 2024. He was first elected president in 2000 and held that post until 2008, when he assumed the post of prime minister due to term limits.