Former Soviet leader Mikhail Gorbachev said on Thursday Russia faced turmoil because Vladimir Putin was unable and unwilling to carry out fundamental reform of a tightly-controlled political system.

Prime Minister Putin, facing the biggest protests of his 12-year rule, has tried to present himself to Russia's 109 million voters as a leader who can carry out gradual reform, after imposing order on the chaos of the 1990s.

But Gorbachev, reviled by many Russians for unleashing the bold reforms that helped sink the Soviet Union, said Putin's continued rule put Russia's future into question.

I don't think he will be able to change course and I am saying we need a change of the entire system, not just handouts or sporadic steps, Gorbachev told students in a lecture at Moscow's International University.

If he cannot change things and change himself, and I think that will be very difficult for him, then I think people will pour out into the streets.

The father of perestroika (restructuring) and glasnost (openness) advised protesters who have come out in their tens of thousands over recent weeks against alleged vote-rigging to ensure their demands were clear and to remain strong.

Protest leaders, a fragmented group of politicians, activists, journalists and bloggers, have called for a re-run of the December 4 parliamentary election which they say was rigged. Official results show Putin's party won 49.3 percent of the vote.

Gorbachev warned protesters to guard against provocateurs who he said would try to incite people to burn down Moscow and thus force a clampdown by the security services.

AGILE

Fielding questions for two hours from students, the 80-year-old former leader of the communist world appeared mentally agile, even joking with one student who asked for a date and advising others to buy his books to find answers.

Gorbachev dismissed the criticism of his countrymen, saying the whole world recognised his achievements. He is feted in the West for ignoring hardliners who advised him to crush growing dissent in the eastern bloc which led to the fall of the Berlin Wall in 1989.

Putin, who has ruled as president and then prime minister since late 1999, has presented himself as the anchor of Russian stability.

But his plan to take over the presidency from Dmitry Medvedev has provoked a backlash from within the elite and from younger urban voters.

Gorbachev criticised what he called the political chemistry of Putin's Russia and said he did not believe the official reason - invalid signatures of support - for the banning of opposition leader Grigory Yavlinsky from the presidential election on March 4.

I think Vladimir Vladimirovich (Putin) is doing everything to win in the first round, Gorbachev said. He is convinced that he will win of course.

(Editing by Andrew Roche)