Libyan leader Muammar Gaddafi has been elected as chairman of the 53-nation African Union.
Col Gaddafi was elected by delegates at the AU summit in Ethiopia.
A BBC correspondent at the summit says Col Gaddafi was seen to be the obvious choice, but some delegates are uneasy about his nomination.
AU spokeswoman Habiba Mejri-Sheikh said Col Gaddafi was elected "by the heads of state in a closed-door session, for a one-year period".
"He is currently addressing the assembly as president, to outline his programme and his intentions," she said.
Col Gaddafi replaces the Tanzanian president, Jakaya Kikwete.
In its earlier sessions, AU delegates called for a lifting of sanctions against Zimbabwe.
The call followed the announcement on Friday that the opposition would be joining a unity government.
On Sunday, the summit debated a Libyan-backed proposal to set up a single government - the United States of Africa.
In a compromise, the summit agreed to transform the African Union Commission, which oversees the body, into an AU Authority that would have a broader mandate, Mr Kikwete said.
"In principle, we said the ultimate is the United States of Africa. How we proceed to that ultimate - there are building blocks," Mr Kikwete said.
Malawi's President Bingu wa Mutharika said governments wanting greater unity could go ahead on their own, without worrying about splitting Africa.
The chairmanship of the African Union is a rotating position held by heads of state for one year.
The BBC's Elizabeth Blunt in Addis Ababa says it was the turn of North Africa to lead the bloc, and Col Gaddafi was seen as the obvious choice. However, some African leaders believe the Libyan leader is too erratic to be AU chairman.
Before he arrived at the summit, he circulated a letter saying he was coming as the king of the traditional kings of Africa and he wanted to be seated as the king of kings, our correspondent says.
Col Gaddafi has previously outlined his vision for African unity.
He wants a single African military force, a single currency and a single passport for Africans to move within the continent.
Last August, a meeting of more than 200 African kings and traditional rulers bestowed the title "king of kings" on the Libyan leader.