Khodorkovsky claims prosecutors have demanded that Aleksanyan, the former vice president of the now liquidated Yukos who is being held in custody in Moscow on charges of embezzlement and money laundering, confess to all charges against him in exchange for medical treatment.
"The legal system in modern Russia has reached a new stage in its development," Khodorkovsky said in a statement.
"My friend, lawyer and former colleague is being coerced into testifying against me, under what is in fact torture. I know from numerous media reports that the seriously ill Aleksanyan is being refused medical treatment, threatening certain death. They are killing him in prison because he, as a courageous and honest man, refuses to lie and slander."
The former oligarch, once Russia's richest man and chief of the country's biggest oil company, said he would continue with his hunger strike in his East Siberian jail until Aleksanyan is released from custody and transferred to a civilian medical facility for in-ward treatment.
The Prosecutor General's Office said in a statement on Thursday that there had been no legal violations in Aleksanyan's treatment in custody, and that his state of health had been proved by a medical inspection to be satisfactory.
"A medical examination of Aleksanyan conducted on January 30 established that his health condition is satisfactory, which permits him to attend court trials," the statement said.
The top prosecutors said the defendant had repeatedly declined to undergo medical examinations, and that there are documents to prove this.
Alla Kuznetsova, first deputy head of the Russian Federal Penitentiary Service's medical department, said on Tuesday that Aleksanyan was receiving all necessary medical treatment in the detention facility.
"Vasily Aleksanyan is receiving medical treatment in full," she said. "Aleksanyan voluntarily signed an agreement for the treatment, but he refused antiretroviral therapy."
Investigators accuse Aleksanyan of embezzling over 8 billion rubles ($329 million) from Yukos production unit Tomskneft as well as shares worth over 12 billion rubles ($493 million) from other oil companies, and of laundering stolen assets.
Khodorkovsky is serving an eight-year prison term for fraud and tax evasion. He has consistently maintained his innocence, calling the accusations against him politically motivated.
On Wednesday a district court in Chita, where Khodorkovsky and his business partner Platon Lebedev are serving their sentences, upheld prosecution's request to extend custody against the two men until May 2, 2008, in relation to a new probe.
The new charges against Khodorkovsky and Lebedev, who were convicted of fraud and tax evasion in 2005, include stealing government shares, illegal oil trade, and laundering $25 billion earned from oil sales in 1998-2004. Both businessmen have denied the allegations, calling them politically motivated.
