Former Soviet leader Mikhail Gorbachev called for Russia's elections to be re-run due to fraud on Wednesday, December 7, as the opposition vowed new rallies contesting the results despite further mass arrests, AP reports.

Riot police in helmets roughly dragged over 550 protestors into detention vans Tuesday evening in central Moscow but the opposition warned they would stage a major protest organized via the Internet at the weekend.

Amid growing international alarm, Gorbachev said the results of Sunday's poll should be invalidated and new elections held due to "numerous falsifications and rigging."

"The results do not reflect the will of the people," Gorbachev, president when the Soviet Union collapsed two decades ago, told the Interfax news agency. "Therefore I think they (Russia's leaders) can only take one decision - annul the results of the election and hold new ones."

Vladimir Putin's United Russia party won the polls with a sharply reduced majority, amid signs the prime minister's once-invincible popularity might be waning.

The opposition says that the ruling party's performance would have been even worse in free polls.