UNITED NATIONS - South Korean Ban Ki-moon takes the oath of office as the eighth U.N. secretary-general at a ceremony in the U.N. General Assembly on Thursday, less than three weeks before he assumes the post from Kofi Annan.

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Both Ban, 62, and Annan, a 68-year-old Ghanaian who has been in office for 10 years, are being honored by the 192-member body with speeches and a resolution. Ban takes over as secretary-general on January 1.

In the oath of office, administered by Assembly President Sheika Haya Rashed Al Khalifa, Ban will swear "not to seek or accept instructions in regard to the performance of my duties from any government or other authority external to the organization."

A former foreign minister, Ban was selected by the 15-member U.N. Security Council in October and then approved by the General Assembly as the first Asian head of the organization in 35 years.

Special guests include Han Seung-soo, under whom Ban served as chief of staff when Han was president of the General Assembly in 2001-2002.

Still little is known about Ban's policies or future appointments, particularly compared to his high-profile predecessor, who traveled widely and spoke out on world issues, sometimes to the chagrin of the United States. Quiet and unassuming, Ban has made few missteps during his life-long career as a Korean diplomat.

John Bolton, the outgoing U.S. ambassador, an early supporter of Ban, made clear that he wanted more of a secretary than a general by saying repeatedly that the U.N. Charter described the job only as the "chief administrative officer."

But in an interview with Reuters after his election, Ban cautioned those who call him low-key not to mistake him for a pushover.

"I may look low-key or (be) soft-spoken but that does not mean that I lack leadership or commitment," he said.

Modesty and humility were considered virtues by Asians, he said, but should not be misunderstood because "I take decisive decisions whenever it is necessary."

Ban will start his five-year term in what Annan has called the world's most impossible job with a daunting agenda that stretches from the threats of nuclear proliferation and terrorism to reform of the United Nations management.

But the future secretary-general showed he was capable of poking fun at himself at a U.N. Correspondents Association dinner, saying he was well aware that in Seoul journalists called him a "Slippery Eel" and in New York, the "Teflon Diplomat."

"These names may reflect different cultures," Ban said. "But they all point to one and the same thing: when I want to, I will elude you as masterfully as any secret agent."

He ended by borrowing from the Christmas carol, "Santa Claus is Coming to Town" and sang: "I'm making a list, I'm checking it twice, I'm going to find out who's naughty or nice. Ban Ki-Moon is coming to town."