Russians cast votes Sunday in parliamentary elections that were plagued by claims of campaign fraud and intimidation of observers.

Popular Russian opposition radio station Moscow Echo and election monitoring group Golos said their websites were the victims of hacking attacks Sunday. Both said their site failures were caused by denial-of-service attacks, which overloaded the sites and made them inaccessible. Several opposition news sites were also inaccessible.

Golos said last week that it had compiled more than 5,300 complaints of election-law violations ahead of the vote, most by Prime Minister Vladimir Putin's United Russia party.

The ruling party is expected to win the elections, but with a reduced majority.

Polls are scheduled to close at 1700 UTC.