Addressing reporters in Bishkek, Tanaev lawyer Kairat Zagibaev read a letter in which his client describes the accusations as politically motivated.
Prosecuting judge Kubanychbek Kerezbaev told RFE/RL's Kyrgyz Service that Tanaev is accused of embezzling state budget funds and abusing his office.
"Those are particularly serious crimes and [he] faces more than eight years of imprisonment," Kerezbaev said. "In any case, a court will decide whether he is guilty or not. The opinion of the prosecution is that his guilt is already proven."
Tanaev -- an ethnic Russian – served as Kyrgyzstan's prime minister from 2002 until March 2005, when street protests overthrew President Askar Akaev.
Tanaev then spent a few months in Russia before returning to Kyrgyzstan to face investigation. He left the country again shortly afterwards, officially to receive medical treatment in Moscow. He remains in Moscow.
Tanaev's lawyer said today that his client would return to Kyrgyzstan as soon as his health improves.