The head of the major international election observer mission in Russia has said there were "serious problems" in the vote that returned Vladimir Putin to the presidency.

Tonino Picula said "there was no real competition and abuse of government resources ensured that the ultimate winner of the election was never in doubt."

Mr Picula headed the short-term observer mission of the Organisation for Security and Co-operation in Europe.

A brief synopsis of the mission's findings did not address Russian independent observers' claims that there were widespread cases of people casting multiple ballots, but said the election "process deteriorated during the vote count, which was assessed negatively in almost one-third of polling stations observed."

Russia's Central Elections Commission says Mr Putin, who was president in 2000-2008, got more than 63% of the nationwide vote, but the independent Russian elections watchdog Golos says incomplete reports from its observers of individual polling station counts indicate he hovered perilously close to the 50% mark needed for a first-round victory.

The OSCE observers' conclusions may have significant bearing on whether Russia's opposition forces will be able to maintain the momentum of the unprecedented large protests they were able to marshal in the past three months.

A protest rally has been set for this evening on Moscow's Pushkin Square.

Some reports say 12,000 police and troops will be on duty to ensure order.