Khodorkovsky and his associate Platon Lebedev, both serving eight-year sentences in Siberia for fraud and tax evasion since 2005, were taken to a pre-trial detention facility in the regional center of Chita in eastern Siberia, where they were expected to be accused of money laundering but no charges followed, Yury Shmidt said.
Prosecutor General Yury Chaika said earlier that Khodorkovsky and Lebedev, both 43, may face new charges if there is sufficient evidence.
"Investigations into the main [Yukos] case are continuing," Chaika said. "Some of its numerous episodes are already in court."
In May 2005, the Moscow Meshchansky Court found Khodorkovsky and Lebedev guilty of tax evasion and grand fraud, and sentenced both to nine years in prison, a term that was later reduced to eight years.
Khodorkovsky is serving his sentence in the town of Krasnokamensk in the Chita Region, and Lebedev is at a colony in the Arctic region of Yamalo-Nenets.