AFP - UN Secretary General Ban Ki-moon called Saturday for national unity in Sudan and ruled out deploying UN peacekeepers in Somalia, on the eve of an African Union summit.

African leaders are officially gathering in Addis Abada for three days of talks on information technology, but esclating violence in Somalia and the looming risk of a secession by south Sudan are set to dominate the summit.

Ban said the coming 12 months would be crucial for Sudan, with elections planned for April -- the troubled African country's first multi-party ballot since 1986 -- and a referendum on independence to be held in January 2011.

In a joint interview with AFP and RFI radio, the UN chief said the United Nations and the African Union had a duty to work for national unity in Sudan and avoid the south seceding.

"The UN has a big responsibility with the AU to maintain peace in Sudan and make unity attractive," he said.

"Whatever the result of the referendum we have to think how to manage the outcome. It is very important for Sudan but also for the region."

"We'll work hard to avoid a possible secession."

Sudan's mainly Muslim north and largely Christian south ended 21 years of civil war in January 2005.

The Comprehensive Peace Accord (CPA), as the deal is known, allowed the creation of a semi-autonomous government for the south and paved the way for April's presidential, parliamentary and regional polls, and next year's referendum.

Sudanese President Omar al-Beshir said this week that Khartoum would recognise the independence of southern Sudan if it chose to secede in the referendum.

North and south are due to draw the 2,100 kilometre (1,300 mile) border between their regions this year -- a delicate issue because of the significant oil reserves in the area.

Ban said the African Union must help ensure the elections and the referendum are carried out in a credible, transparent way.

"There are many fundamental issues: citizenship, borders. All should be resolved so that the referendum could be held peacefully. I'm going to discuss these issues extensively with the African leaders," he said.

Asked about Somalia, Ban again ruled out any deployment of UN peacekeepers until the end of the country's decade-old civil war.

"Practically and realistically it is not possible at this time to deploy a UN peacekeeping force in Somalia," he said.

"We need a peace to keep and now there is no peace."

The African Union has called several times on the UN to take over from its own beleaguered peacekeeping force in Somalia, AMISOM, which has been powerless to stop fighting between Islamist rebels and a weak transitional government.

Other African crises set to loom large at the Addis Ababa summit include the political standoff in Madagascar, which is still in institutional limbo almost a year after Andry Rajoelina took power.

Niger is also on the brink after the president changed the constitution to pave the way for potential lifelong rule, and progress is fragile in Guinea, where an interim administration has taken over from the junta that seized power in December 2008.

Heads of state from the organisation's 53 members are expected to pick a new annual chairman, to take over from Libyan leader Moamer Kadhafi, as soon as the AU's 14th summit kicks off on Sunday.

The system of rotating regional blocs should hand the job to a southern African leader -- with a consensus emerging around Malawi -- but some diplomats fear Kadhafi will put up a fight to hold on to the job.