MOSCOW - JAILED Russian oil tycoon Mikhail Khodorkovsky on Wednesday declared a hunger strike, accusing prison authorities of withholding medical help to force a dying colleague to incriminate him.

In a statement posted on his personal website, Khodorkovsky demanded that officials 'guarantee the life' of Vasily Aleksanyan, a former colleague who supporters say is dying of Aids in a Moscow prison.

Aleksanyan was told that the provision of medical help had been 'directly linked' to his giving evidence against Khodorkovsky, his former boss at the Yukos oil firm, the statement said.

Aleksanyan, 35, was the vice president of Yukos, then Russia's largest oil firm, which Khodorkovsky headed before his conviction in 2005 for massive fraud and tax evasion in a trial that Kremlin critics said was politically motivated.

Mr Aleksanyan appeared separately at a closed hearing in Moscow on Thursday on charges of embezzlement. His lawyer Yelena Lvova said doctors had to be called to the courtroom after he felt ill, the RIA Novosti news agency reported.

Speaking on the radio station Echo of Moscow, President Vladimir Putin's human rights representative Vladimir Lukin called on prosecutors and the prison service to look into the Aleksanyan case and ensure he was treated.

Aleksanyan has been in prison since 2006 for money laundering in a case linked to Khodorkovsky's 2005 conviction for fraud and tax evasion.

Sentenced to eight years in prison, Khodorkovsky now faces additional charges in a new court case. He 'will be punished' if he refuses to eat, the Interfax news agency quoted a senior prison official as saying.

The former Yukos chief could not survive more than two weeks refusing water, former hunger striker and dissident Vladimir Bukovsky told the Echo of Moscow radio station.

Citing his experience in Soviet captivity, Bukovsky said Khodorkovsky would likely be force-fed after about 10 days. -- AFP