Rwanda's Supreme Court has begun hearing appeals in the case of the country's first post-genocide president, who was jailed last June.
Pasteur Bizimungu denied all the charges
Pasteur Bizimungu was sent to prison for 15 years on charges of inciting civil disobedience, associating with criminals and embezzling public funds.
He was arrested in 2002 after trying to form a political party.
His lawyers argue that the jail term should be reduced, while prosecutors want it to be changed to life sentence.
Supporters of Pasteur Bizimungu say the charges against him were politically motivated, but the government in Kigali accused him of stirring up divisions between Tutsis and the majority Hutus.
The former president was tried along with seven other people after he founded a new political party (PDR-Ubuyanja), which was immediately declared illegal by the government.
Mr Bizimungu was one of only a handful of Hutus to join the Rwandan Patriotic Front - the RPF - the rebel movement formed among Tutsi exiles in Uganda.
The RPF took control of Rwanda in July 1994, putting an end to the genocide organised by extremist Hutu leaders that left about 800,000 Tutsis and moderate Hutus dead.
But after his resignation in 2000, Mr Bizimungu became a vocal critic of the RPF-led government.
While the RPF says it has introduced stability and multi-party democracy, its critics claim it has centralised power within a Tutsi elite and crushed potential opponents - by accusing them of promoting ethnic divisions.