UNITED NATIONS  —  South Korean diplomat Ban Ki-moon became the United Nations' eighth secretary-general on New Year's Day as the organization faced a tough array of global issues — from escalating violence in Darfur to the AIDS pandemic.

The 62-year-old career diplomat, who grew up during a war that left his country divided, has promised to make peace with North Korea a top priority.

He will travel there when necessary, he has said, and has cautioned that the reclusive communist nation must be talked to — not just punished with sanctions for its nuclear weapons program.

The United States is certain to press Ban to expand management reforms at the United Nations, which outgoing Secretary-General Kofi Annan began.

The 192-member General Assembly, which controls the U.N. budget and oversees its management, has been reluctant to institute changes that Annan and many experts say are essential to modernize the 61-year-old world body.

In a speech after taking his oath of office Dec. 14, Ban said he will work to build "a more peaceful, more prosperous and more just world for succeeding generations."

His first priority, he said, will be to restore trust in the United Nations, whose reputation has been battered by the oil-for-food scandal in Iraq, corruption in the U.N.'s purchasing operations and sexual abuse by U.N. peacekeepers.

"I will seek to act as a harmonizer and bridge-builder," Ban said. "And I hope to become known ... as a secretary-general who is accessible, hardworking, and prepared to listen attentively."

Ban officially became secretary-general at the stroke of midnight, but no official ceremony was scheduled.

He won't get to move into his official residence — an 85-year-old neo-Georgian town house on New York's fashionable Sutton Place — due to renovations, the first since 1950.

The General Assembly recently approved $4.9 million to modernize the residence's heating, air conditioning, plumbing, kitchen and security. The work is expected to take about nine months.

Ban defeated six other candidates for U.N. chief and won final approval from the General Assembly in October. Since then, he has been meeting with a wide range of people inside and outside the U.N. to prepare for the job.

On Sunday, Ban announced his first two appointments. He named veteran Indian diplomat Vijay Nambiar as his chief of staff, and award-winning Haitian journalist Michele Montas as his spokeswoman.

Ban said in a statement Sunday that he will make more appointments in the coming days. The most important will be his choice for deputy secretary-general — widely expected to be a woman from a developing country.

The new secretary-general's first day at U.N. headquarters will be Tuesday, when he plans to meet with U.N. staff after an official welcome and sit for his official portrait.

Ban will be the first Asian to lead the organization in 35 years. It also will mark a milestone for South Korea, which only joined the United Nations in 1991 and still has U.N. troops on the tense border with North Korea.