Russian President Dmitry Medvedev said at a press conference in Berlin on Thursday that Khodorkovsky could file a petition for a pardon, but the issue was not one for discussion at an international level.
"I do not know whether Mikhail [Khodorkovsky] will decide to file a petition. I have not discussed this issue with him," Yuri Shmidt said, adding that he considered his client to be innocent.
A court in the Siberian city of Chita earlier extended a probe into a second set of charges against Khodorkovsky and his ex-business partner Platon Lebedev, who is also serving eight years on similar charges, until August 2.
The latest charges against Khodorkovsky and Lebedev, both convicted in 2005, include stealing government shares, illegal oil trading, and laundering $25 billion earned from oil sales in 1998-2004.
Both have maintained their innocence of all the charges. Khodorkovsky has said his imprisonment was a direct result of his support for Russia's tiny pro-Western opposition.
Yukos, once Russia's largest independent oil producer, collapsed after claims of tax evasion in 2004 led to the company being broken up and sold off to meet creditor claims. The bulk of its assets were bought at liquidation auctions by government-controlled oil company Rosneft. Yukos was officially dissolved in 2007.
