The Kremlin barred the last liberal opposition candidate from Russia's presidential election yesterday, as Vladimir Putin took his revenge on a former ally who had turned into a fierce critic.

Mikhail Kasyanov, who was Mr Putin's Prime Minister for four years until 2004, was forced off the ballot after the Central Election Commission ruled that thousands of signatures in support of his candidacy had been forged. He had virtually no chance of winning, but supporters said that his expulsion from the contest showed that the Kremlin was unwilling to tolerate any criticism of Mr Putin and his chosen successor, Dmitri Medvedev.

Mr Medvedev's only rivals in the March 2 election will be the Communist Party leader Gennady Zyuganov, the anti-Western nationalist Vladimir Zhirinovksy and Andrei Bogdanov, the head of the tiny Democratic Party.

Mr Medvedev's victory is all but certain. State television is giving blanket coverage to him and polls show that his support has climbed to 80 per cent since Mr Putin endorsed him last month.

The rejection of Mr Kasyanov, 50, will heighten concerns in the United States and Europe that the election is little more than a rubber-stamp exercise to allow Mr Putin to retain power. He is barred by the constitution from seeking a third consecutive term as President, but has said that he will serve as prime minister under Mr Medvedev. Critics say that Mr Medvedev, 42, will be little more than a figurehead while Mr Putin runs the country.

Mr Kasyanov called on Russians to boycott the election in protest.

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