MOSCOW - Russia's supreme court has trimmed by two months the 11-year prison camp term of former oil tycoon Mikhail Khodorkovsky over a conviction which supporters say was ordered by the Kremlin.

The court rejected an appeal from the defence to quash his 2010 conviction for money laundering and embezzlement, and to free Khodorkovsky.

Instead, it slightly reduced his jail term to 10 years and 10 months.

The ruling means that Russia's most famous convict, who was first detained in October 2003, should now walk free in August 2014. His co-accused, Platon Lebedev, received an identical reduction of two months and should be released in May 2014.

"By two months - I feel shame for the country. I had awaited an honest answer," said Khodorkovsky's father Boris who was present at the hearing, quoted by the Interfax news agency.

Russia's former richest man, who built up the now defunct Yukos energy firm into Russia's biggest oil company, spoke via video link from his remote prison colony in northwestern Russia at the appeal hearing.

Khodorkovsky's defence team argued in the appeal that he and Lebedev were convicted in 2010 on charges that were known to be false and that were invalid from the start.

The supreme court ruling concerned Khodorkovsky's second conviction in 2010, not his first conviction from 2005 on fraud and tax evasion charges. The two sentences are running concurrently.

Khodorkovsky's lawyer Vadim Klyuvgant told Russian news agencies that the defence planned to appeal the verdict with the praesidium of the supreme court.

In a statement to the court by the video link, Khodorkovsky denounced what he said was the use of Russian prosecutors and investigators as an "instrument of domestic politics in Russia".

"The result is catastrophic," said Khodorkovsky, who was shown on the video speaking behind a mesh grill wearing his laminated prison identity card.

"We are not talking about implementing the law, we are talking about a readiness to sacrifice the reputation of the legal system for the sake of a new prison sentence for an opponent of the authorities," he added.

"For me, it was and is always important to obtain justice in the motherland" he told the judge.

Khodorkovsky and Lebedev - head of the former Menatep bank that formed a part of Khodorkovsky's conglomerate - were jailed in 2005 on fraud and tax evasion charges. Khodorkovsky turned 50 in jail this year, while Lebedev is 56.

Shortly before their scheduled release, their stay in jail was extended until 2017 during a second controversial trial in 2010 in a move that drew strong condemnation from the West.

Their sentences were then reduced by the Moscow city court to 11 years.

However, some activists have expressed fear that new charges could yet be brought against Khodorkovsky as the Kremlin considers him such a dangerous potential opponent.

Khodorkovsky's supporters have long argued both sets of charges were trumped up by the state to punish him for daring to finance political opposition to President Vladimir Putin and ridiculed the circumstances of the second trial.

Mr Putin, who has never made a secret of his dislike of Khodorkovsky, said even before the verdict in the second trial was announced that "a thief should be in prison," drawing criticism that he was interfering in the process.

Khodorkovsky is being held in a prison colony in Karelia in north-west Russia, while Lebedev is in the far north Arkhangelsk region.

In July, the European Court of Human Rights ruled the men's first trial had been unfair but said that the judge was impartial.

Pro-opposition observers link the Khodorkovsky case to a general crackdown on the opposition under Putin which last month saw protest leader Alexei Navalny handed a five year sentence in an embezzlement case.