International monitors from the Organization for Security and Cooperation in Europe also questioned the fairness of Sunday's parliamentary elections, CNN reported.

The Novosti news agency reported with 98 percent of votes counted, United Russia received 64.1 percent of the vote, the Communist Party 11.6 percent, the ultranationalist Liberal Democratic Party 8.2 percent and the loyalist A Just Russia 7.8 percent.

Communist Party leader Gennady Zyuganov called a news conference to criticize the results and Putin's party.

"This group has come up with 20 ways of humiliating the people," Zyuganov said.

Among the changes the party instituted before the vote was abolishing the "none of the above" option on ballots, increasing parties' minimum election threshold from 5 percent to 7 percent and canceling the minimum voter turnout requirement, Novosti said.

Kremlin spokesman Dmitri Peskov told CNN the complaints were groundless.

"What we faced here was a free and democratic election campaign," Peskov said. "And the fact that we now, according to preliminary results, are expecting a three- or four-party parliament shows that this was really a race."