Mikhail Khodorkovsky vowed on Tuesday to fight for his freedom and the "freedom of the whole of Russia" after he was sentenced to serve nine years in prison for fraud and tax evasion.
Once Russia's richest man, Mr Khodorkovsky made clear he had not renounced his ambitions to reshape Russia's political landscape. "I will work together with those who want to and are able to talk openly about the country and the people and our shared present and future," he said in a statement.
Platon Lebedev, Mr Khodorkovsky's business partner, was found guilty of the same charges and given the same sentence.
The case has been viewed as an attack by the Kremlin on a businessman who was using his wealth to gain political influence. The Kremlin has also renationalised part of Mr Khodorkovsky's Yukos oil company in part payment of a massive $28bn (€22.7bn) back tax claim.
President George W. Bush said on Tuesday he had expressed concerns about the case to Russia's president Vladimir Putin. "It appeared to us, at least people in my administration, that he had been adjudged guilty prior to having a fair trial," Mr Bush said. "In other words, he was put in prison and then tried."
Russia's prosecutor-general made clear the verdicts were not the end of the assault on Mr Khodorkovsky, saying it would soon bring new charges.
The prosecutor's office has said it is preparing money laundering charges against Mr Khodorkovsky and Mr Lebedev.
Lawyers said the two men would appeal. They are expected to take their case to the European Court of Human Rights.
The nine-year term was one less than the maximum 10 years demanded by the prosecution.