The banner is on the roof of a building on the opposite bank of the Moscow River. An activist group called Solidarity says it put it there.

Prime Minister Vladimir Putin is tipped to win the presidential election on 4 March. He had two terms as president, in 2000-2008.

Fraud allegations marred December's parliamentary poll won by his party.

Ilya Yashin, an activist with Solidarity, said the anti-Putin banner which appeared on Wednesday measured 140 sq m (1,507 sq ft).

The yellow banner showed a big black cross over a sketch of Mr Putin's face.

International observers, as well as Russian opposition activists, voiced concern about reports of ballot-stuffing and other irregularities in the December vote.

Mr Putin insisted the parliamentary results were valid and scoffed at some of his opponents.

But he has asked Russia's central electoral commission to install web cameras at all polling stations for the March vote.

Tens of thousands of activists have attended opposition rallies in recent weeks and another such event is planned for Saturday. Many of them are urban professionals connected through online social networks.

bbc.com