Russia's election commission head says results from voting for parliament in a Siberian region could be annulled if allegations of vote fraud there are confirmed, reports AP.
Ella Pamfilova's statement came Sunday as Russians cast ballots for the State Duma, the lower house of parliament.
The pro-Kremlin United Russia party is expected to retain its dominance and the three other largely cooperative parties in the current parliament are also expected to win seats.
Russian officials are concerned that widespread allegations of vote fraud could spark protests similar to the massive demonstrations after elections in 2011.
A candidate from the liberal Yabloko party in the Altai region of Siberia told state news agency Tass that young people were voting in the name of elderly people unlikely to come to polling stations.
Pamfilova was later quoted by Russian news agencies as saying complaints had not been received from other regions. But the election monitoring group Golos said on its website that the organisation and local election commissions had received reports of violations in several regions, including in Moscow.
The extent of the alleged violations and the credibility of the reports could not immediately be determined.
Pamfilova is a well-known human rights activist whose appointment five months ago to head the election commission brought expectations that this year's vote would see fewer controversies about violations than in previous elections.
This election is a departure from the two previous votes for the Duma, in which seats were distributed on a national party-list basis; this year, half the seats are being contested in single districts. Independent candidates were also allowed, although only 23 met the requirements to get on the ballot, according to the elections-monitoring mission of the Organisation for Security and Cooperation in Europe.
Pre-election polling by the independent Levada centre indicated that only the four parties now in parliament -- United Russia, the Communists, the nationalist Liberal Democrats and A Just Russia -- would get enough nationwide votes to be allotted seats. Prospects for the single-district races were unclear.
In Moscow, a man claiming to have a bomb threatened to blow up a polling station. Mayor Sergei Sobyanin said on Twitter that the man was quickly arrested and Russian news agencies said no bomb was found.
In the Ukrainian capital Kiev, dozens of right-wing protesters gathered around the Russian embassy, where a voting station was set up. At least one demonstrator was detained in a scuffle with police.