Hillary Clinton, the US secretary of state, issued a statement on Monday saying the oligarch's conviction raised "serious questions about selective prosecution - and about the rule of law being overshadowed by political considerations."

But a foreign ministry spokesman in Moscow said: "Judgements about some kind of selective application of justice in Russia are without foundation." He added: "We are counting on everyone minding his own business – both at home, and in the international arena."

Khodorkovsky, 47, and his business partner, Platon Lebedev, 54, were found guilty by a Moscow court yesterday of theft and money laundering, in a trial that critics say is revenge for the tycoon questioning a state monopoly on oil pipelines and propping up political parties that oppose the Kremlin.

Clinton's censure was echoed by politicians in Britain and Germany. Catherine Ashton, the European Union's foreign policy chief, urged Moscow to "respect its international commitments in the field of human rights and the rule of law."

Viktor Danilkin, the trial judge, said the two men had been found guilty when he began reading his 250-page verdict yesterday. But their fate remains unclear because sentencing will not take place until he finishes the text, which could take several days.

The Russian foreign ministry spokesman hit back at criticism from abroad, saying that "in connection with statements from Washington and a series of European capitals, we would like to underline once more that this question is a matter for the judicial system of the Russian Federation. Attempts to place pressure on the court are unacceptable."

The trial related to "serious accusations of tax avoidance and laundering of criminally received income. In any country such deeds require criminal punishment. In the United States, by the way, life sentences are given for these acts."

Similar prosecutions were common, the spokesman claimed. "Thousands of cases regarding the responsibilities of entrepreneurs before the law are considered in Russian courts," he said.

The spokesman referred to comments by Dmitry Medvedev on Friday, saying Russia's president had "stressed that nobody has the right to interfere in the prerogatives of the judicial authorities."

Khodorkovsky and Lebedev have been in jail on earlier fraud and tax evasion charges since 2003. They are due for release next year but prosecutors in the current trial want them to stay in jail until 2017.

Several hundred protesters gathered around the trial court in Moscow's Khamovniki district yesterday shouting, "Shame!" and "Russia without Putin!" as proceedings got under way inside.

Danilkin resumed reading his verdict today as police closed streets around the court to traffic.

Asked about Khodorkvosky's second trial earlier this month, Vladimir Putin, the prime minister, replied: "A thief should be in jail."

Khodorkovsky's backers condemned that as open pressure on the court, but Putin later claimed he was referring only to the businessman's first conviction.

In her comments yesterday, Clinton said the case had a "negative impact on Russia's reputation for fulfilling its international human rights obligations and improving its investment climate."