US President George W Bush has said he expressed concern about Russia's parliamentary elections in a phone call with President Vladimir Putin.
Mr Putin's United Russia party won 315 seats in the vote
"I said we were sincere in our expressions of concern about the elections," Mr Bush told reporters at a news conference in Washington.
Mr Putin's United Russia secured a big majority in Sunday's election, which the Kremlin said was conducted fairly.
But opposition parties and Western observers said the poll was not fair.
The Communist Party was the only opposition party to win seats in the State Duma, Russia's lower house.
Liberal opposition parties failed to reach the 7% threshold to enter parliament.
Election officials said on Tuesday that pro-Kremlin parties had secured 393 out of 450 seats in the Duma, with 57 seats going to the Communists, Reuters news agency reported.
The Kremlin has insisted that the vote was fair and said it demonstrated Russia's political stability.
But a joint observer team of the Organisation for Security and Co-operation in Europe (OSCE) and the Council of Europe has criticised "abuse of administrative resources" and "media coverage strongly in favour of the ruling party".
The Bush administration has called on Russia to investigate whether the vote was manipulated.