Russian Prime Minister Vladimir Putin faces a growing challenge to his plan to return to the presidency next year amid continued opposition protests.

Demonstrations have been held over the past two weeks calling for a recent parliamentary election to be re-run on the grounds that the Kremlin fixed the results in Putin’s favour.

Opposition activist Yevgenia Chirikova has spoken out against Putin’s United Russia party.

“I am happy to have lived enough to see Russians go out into the street,” she told a crowd in Moscow.

Organisers say at least 100,000 people attended an anti-Kremlin rally on Saturday.

Police put the number closer to 30,000.

In an interview with the Echo of Moscow radio station, Mikhail Gorbachev, who resigned as president of the Soviet Union twenty years ago on Sunday, again urged Putin to step aside.

“I would advise Vladimir to step down now. Three terms is enough. Two terms as president and another term as prime minister. That’s enough. Because otherwise powerful inner circles and clans begin to take shape.”

The former Soviet leader once backed Putin but he has been increasingly critical since the ex-KGB man announced that he would run again for his old job of president, currently held by his hand-picked successor Dmitry Medvedev.