A statement released by the Kremlin said Mr. Medvedev had also asked the prosecutor general to review the conviction of Mr. Khodorkovsky’s former colleague, Platon Lebedev, and 30 other people.

Image Platon Lebedev Credit... Misha Japaridze/Associated Press

Though his prominence has waned, Mr. Khodorkovsky remains a symbol of opposition to Mr. Putin. His release from prison is among the top demands of a protest movement that arose recently as an unexpected challenge to Mr. Putin’s authority.

Mr. Khodorkovsky would have been eligible for parole this year on an initial conviction on charges of tax evasion in 2005. But he was convicted on separate embezzlement charges in 2010 and sentenced to six more years in prison.