The Russian Prosecutor General's Office has brought new charges against the former head of the Yukos company, Mikhail Khodorkovsky, according to his lawyer.
Mr Khodorkovsky and his associate Platon Lebedev are accused of embezzlement and money laundering.
The new charges were brought by the prosecutors of the Russian city of Chita in Eastern Siberia where the two are currently in prison.
Mikhail Khodorkovsky, who used to be on top of the list of Russia's richest people, is currently serving an 8-year prison term for fraud and tax evasion.
Both men could have been given early release in 2008. If the new charges are upheld, this could mean more years in prison for both men.