UNITED NATIONS (AP) - U.N. Secretary-General Kofi Annan, whom the U.S. ambassador once described as ``an international rock star of diplomacy,'' announced Thursday that he will seek a second five-year term at the helm of the world body.

``If asked, I am ready to serve,'' Annan said, ending months of speculation and officially letting the world in on the worst-kept secret at the United Nations

Last week, the secretary-general, who is from Ghana, got a strong endorsement from the 53-nation African group at the United Nations. The group urged him to run and pledged to campaign for him.

With Annan in the race, the two key questions now are whether Asian nations also will submit a candidate, and who will get the support of the five veto-wielding permanent members of the Security Council - the United States, Russia, China, Britain and France.

By tradition, the secretary-general's job rotates every 10 years by region, and it's now Asia's turn to propose a candidate.

But Africa's 10-year term was split after the United States successfully lobbied to prevent Annan's predecessor, Boutros Boutros-Ghali of Egypt, from taking a second term. And a quiet campaign has been under way for months to pressure Annan to stay in the job for another five years, because he is highly regarded by many nations.

Before stepping down in January, U.S. Ambassador Richard Holbrooke called Annan ``an international rock star of diplomacy'' and said he was the best secretary-general in the 55-year history of the United Nations, a view echoed by representatives of several other key countries.

But Annan has also faced criticism for trying to negotiate with Iraqi President Saddam Hussein over access to suspected weapon sites, and for promoting a new policy of ``humanitarian intervention'' to prevent major internal human rights violations. Many countries opposed the concept as an infringement on their sovereignty.

China's deputy U.N. ambassador, Shen Guofang, said last week that some Asian delegations want the next secretary-general to be an Asian. The Asian group is expected to meet again within the month, he said.

But diplomats said the region is divided on a candidate, and there is no obvious leading contender.

According to one key diplomat, the five permanent council members all will support Annan for a second term. But there will be no outright endorsement until the council sees whether any other candidates emerge to challenge him.

Annan, who celebrates his 63rd birthday on April 8, is the seventh secretary-general and the first to be elected from the ranks of U.N. staff. He was the U.N. undersecretary-general for peacekeeping when he was tapped for the top job. His current term expires Dec. 31.

In backing Annan, the Africans cited his vision for the 21st century that was endorsed by more than 150 world leaders at last September's Millennium Summit. They pledged to send every child to primary school, deliver millions from destitution and halt the spread of AIDS and other major diseases by 2015.

The African ambassadors also singled out Annan's leadership in reforming the United Nations, in overhauling U.N. peacekeeping, in raising often ignored critical issues, in getting U.N. bodies to work together, in reaching out to the business community and voluntary organizations - and in giving the world body ``a public face.''