Former Moscow Mayor Yuri Luzhkov has accused Russian President Dmitry Medvedev of acting "like a dictator".
In a BBC interview, Mr Luzhkov also criticised preparations for parliamentary elections due in December, predicting fraud.
The former mayor was once one of Russia's most influential politicians but was sacked just over a year ago after falling out with the Kremlin.
The Russian authorities have since accused him and his wife of corruption.
He said December's vote would not be free or fair and that regional governors would be under pressure to provide a good result for the governing United Russia party.
He said the party, of which he was once a high-ranking member, would not be able to win the elections without a massive fraud.
"There's no competition; there are no alternatives to choose from," he told BBC Russian.
"Unfortunately we already know the outcome and we know who will be governing Russia next year."
Mr Medvedev, who has held the presidency since 2008, is widely expected to become prime minister.
Mr Luzhkov considers Prime Minister Vladimir Putin, who is likely to become Russia's next leader in presidential elections, the more democratic face of the ruling duo in the Kremlin.
"Despite the fact that Putin is widely regarded in the West as less democratic than Medvedev, in fact Putin is more tolerant towards any sort of dissent," he said
"Medvedev shows inclinations to suppress any dissent," he said. "Medvedev would make as inefficient a prime-minister of Russia as he was a president."
'Matter of honour'
Russian officials have responded by accusing the ex-mayor of '"limitless corruption" during his 18 years in office.
Last week Russian prosecutors demanded that Mr Luzhkov appear for questioning as a witness in a criminal case relating to deals conducted by the Bank of Moscow, which was part-owned by the city's government during Luzhkov's term in office.
The bank's director, Andrei Borodin, has fled Russia and currently lives in London.
The investigation also concerns business interests of Mr Luzhkov's wife, Elena Baturina.
She was once Russia's richest woman, but has sold her construction companies and has left the country.
The former mayor, currently travelling outside Russia, has been rumoured to be seeking a permanent move abroad. Both he and his wife deny the allegations of corruption.
However, 75-year-old Mr Luzhkov stressed that he remained a Muscovite and would return to face the investigators.
"This is a matter of honour to me. If I didn't, that would give my adversaries an easy way of proving that I am guilty," he said.