With 30.2% of votes counted, President Vladimir Putin's United Russia party has garnered 63.6%, followed by the Communists with 11.3%, the ultranationalist Liberal Democratic Party (LDPR) with 9.6%, and A Just Russia with 7.2%.
Communist Party leader Gennady Zyuganov said the LDPR and A Just Russia are "direct helpers and sidekicks of United Russia."
"[LDPR leader Vladimir] Zhirinovsky's list is coordinated in the Kremlin. The same is true of [A Just Russia leader Sergei] Mironov," the Communist leader said.
"This is not a parliament, but a branch of the Kremlin, a department of the government," he said.
The Communist Party said earlier it is preparing lawsuits to contest the results of the elections, irrespective of how many seats the party wins.
"A group of our lawyers have already begun preparing lawsuits for the Supreme Court to contest the results of voting," said the head of the party's legal service, Vadim Solovyev.
"The barrage of violations exceeds all acceptable norms," he added.