Russian Prime Minister Vladimir Putin on Tuesday admitted that there were some voting irregularities in his presidential election victory.
Putin said during a visit to a Kremlin-backed monitoring centre that an investigation would be held.
“There were, of course, violations. We need to identify them all, weed them out and make everything clear to everyone that the situation is being monitored and is under control,” Putin said.
Putin’s return to the presidency has been criticised by former Soviet Union leader Mikhail Gorbachev.
He told the Echo of Moscow radio station that the government had side-stepped its own measures that it put in placesto reduce the risk of voting fraud.
Opposition protesters are planning more demonstrations on Saturday.
Activist blogger Alexei Navaly said that thousands of people would descend upon the streets of Moscow and would not leave until real democratic reforms were achieved.
Police arrested more than 500 demonstrators in the Russian capital and St Petersburg.
Around half of them have already been freed.