Prime Minister Vladimir Putin said on Tuesday he would reshuffle the Russian government after a March 4 presidential election he is almost certain to win.

There will of course be a significant renewal of personnel in the government, Putin told members of his ruling United Russia party. He added that there would also be changes of regional governors.

The rouble weakened against the dollar and Russia's main MICEX stock index fell by 1.6 percent after Putin's comments, on market concerns over possible political fallout from Sunday's parliamentary election, traders said.

Putin's ruling party won only about half of the votes cast, and saw its majority cut to 13 seats in the worst electoral upset of his 12-year rule.

When asked by one party member if the old Putin or the new Putin would be returning to the Kremlin after the presidential election, Putin said he would adjust to society's demands for modernisation.

Several thousand Russians took to the streets on Monday to demand an end to Putin's rule and to protest against the parliamentary elections which they say were rigged.

The Kremlin says they were fair but the United States said it had serious concerns about the conduct of the election. International election observers said there had been serious indications of ballot box stuffing.

(Reporting by Gleb Bryanski, writing by Guy Faulconbridge, editing by Douglas Busvine)