A key rebel leader in the Sudanese region of Darfur has threatened to boycott upcoming peace talks if more than two rebel groups are invited.
Khalil Ibrahim, head of the Justice and Equality Movement (Jem), said only his group, a united Sudan Liberation Army and the government should participate.
The Jem would not attend if splinter groups were present as talks would be chaotic, Mr Ibrahim said.
Since last year, Darfur rebels have split into as many as 12 factions.
Mr Ibrahim criticised the African Union and United Nations envoys - Jan Eliasson and Salim Ahmed Salim - as being ill prepared for the talks, which are scheduled to begin in the Libyan capital on 27 October.
"The AU and UN mediation until now have failed to detail very precisely who will be invited to the peace talks," Reuters news agency quotes him as saying.
"If the mediation fails to take this decision by 27 October, then Jem is not attending the peace talks. We don't want to start with chaos."
The BBC's Amber Henshaw says many fear the talks are doomed from the outset because the factions are not united and another key leader, Abdul Wahid al-Nur of the Sudan Liberation Army, is refusing to take part.
Diplomats are concerned that without his approval any deal that is signed will not be backed by thousands of Abdul Wahid's supporters in Darfur, our correspondent says.
At least 200,000 people have died and some 2m forced from their homes during the four year conflict in Darfur.