The rebel group JEM issued a statement Tuesday saying it will not attend Saturday's talks in Sirte, Libya.
Several other rebel factions have also indicated they will boycott the talks. These include a Sudan Liberation Movement faction led by Ahmed Abdelshafi and the Sudan Liberation Movement-Unity faction, as well as influential Sudan Liberation Movement leader Abdelwahid al-Nur.
Researcher Mariam Jooma, with the Institute for Security Studies in Pretoria, South Africa, says she believes the absence of so many key figures will make it difficult to achieve results.
Jooma says, "The rebel factions are not wanting to attend because they believe that they still have not reached a consensus view as to what their demands are."