Complaints of election violations are increasing as Russians went to the polls for a new national parliament on Sunday.
The voting for the 450 seats in the State Duma, the lower house of parliament, was not expected to substantially change the distribution of power, in which the pro-Kremlin United Russia party holds an absolute majority.
However, the perceived honesty of the election could be a critical factor in whether protests arise following the voting.
Massive demonstrations broke out in Moscow after the last Duma election in 2011, unsettling authorities with their size and persistence.
"Information about violations is coming constantly from various regions," Interfax news agency quoted Ilya Shablinsky, a co-ordinator of observers for the presidential Council on Human Rights, as saying.
Among the potential violations he cited were long lines of soldiers voting at stations where they were not registered and voters casting their ballots on tables instead of curtained-off voting booths.
Election monitoring group Golos also said it was receiving complaints. A video posted on YouTube appeared to show a poll worker in the southern Rostov region dropping multiple sheets of paper into a ballot box.
On Sunday morning, Russia's election commission head said results from voting in a Siberian region could be annulled if allegations of vote fraud there are confirmed.
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.
Elections commission head Ella Pamfilova was later quoted by Russian news agencies as saying complaints had not been received from other regions.
The 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 Co-operation in Europe.
Pre-election polling by the independent Levada Centre indicated 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.