United Nations Secretary General Ban Ki Moon has urged African leaders to work for national unity in Sudan to prevent the south of the country seceding from the north.
The African Union is holding a summit in the Ethiopian capital, Addis Ababa.
Mr Ban said both the UN and AU have a big responsibility to maintain peace in Sudan and make unity attractive.
A referendum is due next year on whether the south, which has oil, should become independent.
President Omar al-Bashir has said he will accept the result of the poll, even if the south votes for independence.