ADDIS ABABA: UN and African Union leaders, gathered here for the second and final day of an AU summit, were discussing post-referendum Sudan and the future of Somalia after the transitional government's mandate expires in August, officials said Monday.

UN chief Ban Ki-moon is chairing the meeting. Those taking part include Sudan President Omar al-Bashir, south Sudan leader Salva Kiir, Ethiopian Prime Minister Meles Zenawi and African Union Commission chief Jean Ping.

Also in attendance are South African President Jacob Zuma and officials from the Intergovernmental Authority on Development (IGAD), a six-member regional grouping.

Ban said Saturday he would meet with Somali President Sharif Sheikh Ahmed ahead of the mini summit.

He insisted that Somalia, which started its descent into chaos exactly 20 years ago with the ouster of Mohamed Siad Barre, has not been overshadowed by the continent's more recent crises.

"I have been discussing this matter, very, very hard, all the time. It has not been overshadowed," the secretary general said.

"The Somalian people have been suffering from political instability for almost the last 20 years."

Officials have made it clear that while Sudan's independence vote went off smoothly, with almost 99 percent of south Sudanese voting to secede according to results published Sunday, Sudan cannot rest on its laurels.

"What is important at this time, is that the parties should engage immediately to address all the post-referendum issues," Ban said, citing border demarcation, citizenship, security matters and the sharing of wealth, as well as the status of the contested border district of Abyei.

"The United Nations will engage, whatever the results may be, with the people and government of Sudan."

The officials will also discuss Darfur, the troubled region of western Sudan, on the understanding that a return to calm there is a prerequisite for peace in the new south Sudan.