Medvedev has chosen not to participate in the TV debates. As Putin's favoured candidate, he is expected by analysts to receive blanket coverage elsewhere.

In the only sign of the official campaign, Rossiyskaya Gazeta, the state newspaper, carried the programme of Medvedev's United Russia party, concluding: "We consider ourselves continuers of the patriotic tradition of the whole of Russia's 1,000-year statehood."

'Innovative economy'

On Friday, Putin was at Medvedev's side on the unofficial campaign tour, telling regional leaders in the southern town of Novocherkassk that they had to invest in people.

"An innovative economy is impossible without investment in people, that is, in education and health care," Putin said, flanked by Medvedev.

Having served two consecutive terms as president, Putin is obliged to step down in May under the terms of the constitution.

But he is expected to retain major power thanks to his protege and has said he will take up the post of prime minister.

Critics such as the Other Russia movement of Garry Kasparov, the former chess champion, accuse the Kremlin of skewing the race by using electoral law to remove serious opponents while ensuring Medvedev disproportionate coverage.

The other three candidates are Vladimir Zhirinovsky, the ultra-nationalist leader of the Liberal Democratic Party of Russia, Gennady Zyuganov, the Communist party leader, and Andrei Bogdanov, Democratic party leader.

Zyuganov and Zhirinovsky, though sometimes critical of the powers that be, have a record of loyalty in parliamentary votes.

Bogdanov, a self-declared liberal, is virtually unknown in public life.