A Moscow court swiftly rejected an appeal by the former oil tycoon Mikhail Khodorkovsky on Thursday, deliberating for an hour before affirming his conviction on fraud and tax evasion charges.

After a one-day hearing, the Moscow City Court reduced Khodorkovsky's prison sentence from nine to eight years and ordered the sentence carried out immediately. "The punishment will come into force," Judge Vyacheslav Tarasov said. "The hearing is over. I ask the guards to take the convicted man away."

The decision ended Khodorkovsky's unusual plan to run for parliament in a December by-election, because Russian law bars convicted prisoners from seeking elective office.

"Not only am I not guilty but also a crime was never committed," Khodorkovsky said in a statement to the court before the decision was announced. "My guilt has been recognized not by a court but by a clutch of bureaucrats."

Khodorkovsky, 42, smiled wanly as he looked toward his elderly parents and his attorneys before he was led away in handcuffs.

He has been held in Moscow since shortly after his arrest in Siberia in October 2003, when masked commandos stormed his private plane at an airport. He is likely to be transferred to a prison facility away from Moscow, where he has been able to communicate with the news media and others through his attorneys.

Khodorkovsky charges that his arrest and prosecution were part of a government effort to break up Yukos Oil Co., the conglomerate he founded and once headed. The company has largely been dismantled in a series of parallel legal actions concerning tax evasion, and its key assets have been taken over by a state-owned oil company. Once valued at close to $40 billion, Yukos is now struggling to survive against further state and private claims.

Khodorkovsky's supporters have condemned his prosecution as a Kremlin-orchestrated case designed to crush a potentially dangerous political opponent. Once Russia's richest citizen, Khodorkovsky before his arrest had been staking out a political role in opposition to President Vladimir Putin.

Khodorkovsky's business partner, Platon Lebedev, was also convicted on tax charges. His nine-year sentence was also reduced by one year, although he had declined to formally appeal and had derided the process as a farce. The court also struck down or modified some of the charges against Khodorkovsky and Lebedev.

Khodorkovsky's attorneys said they would continue to seek redress in higher courts and were likely to take the case to the European Court of Human Rights in Strasbourg, France. That court's rulings are binding on Russia, a signatory to the European Convention on Human Rights. Khodorkovsky must first appeal to the Russian Supreme Court, which is not obliged to take the case.

"The current hearings are a parody of justice," one of Khodorkovsky's attorneys, Yuri Schmidt, said after the verdict. He called the one-year reduction in his client's sentence a "cosmetic facelift" and "a pure act of propaganda."

Prosecutors insisted that they had successfully put a rogue businessman behind bars. "We are generally satisfied with the Moscow City Court ruling," said Dmitri Shokhin, one of the prosecutors. "It was the right of the court to reduce the prison term."

Mikhail Khodorkovsky, former head of the Russian oil giant Yukos, listens from the defendant's guarded glass cage.