UNITED NATIONS - South Korea's Ban Ki-moon was sworn in as the next UN secretary general at a General Assembly ceremony during which he vowed to be "a harmonizer and bridge-builder" and build on the legacy of the incumbent, Kofi Annan.

United Nations Secretary General-designate Ban Ki-Moon of South Korea speaks to the media after he was sworn in, at UN headquarters in New York. [AFP]

"I, Ban Ki-moon, solemnly swear to exercise in all loyalty, discretion and conscience the functions entrusted to me as secretary general of the United Nations," said Ban as he took the oath, his left hand resting on the UN charter.

The 62-year-old South Korean is to officially take up his post on January 1, 2007.

"I add my voice to the many tributes that have been paid to you today," Ban told Annan, who is to step down on December 31 after completing two five-year terms.

Ban vowed to build on the legacy of the outgoing Ghanaian UN chief, adding that one of his priorities would be to "breathe new life and inject renewed confidence into the sometimes weary (UN) Secretariat."

"By strengthening the three pillars of our United Nations -- security, development and human rights -- we can build a more peaceful, more prosperous and more just world for succeeding," the South Korean former foreign minister said to loud applause from the packed assembly.

Mindful of the recent corruption and sexual abuse scandals that have tarnished the world body, Ban promised to "set the highest ethical standard" and to "lead by example".

"My first priority will be to restore trust," he added, in apparent reference to the polarization between rich and poor UN member states over UN reforms. "I will seek to act as a harmonizer and bridge-builder."

Addressing a news conference later in the day, the secretary general-designate described the tragedy in Sudan's Darfur region as "unacceptable" and pledged to be personally engaged in efforts to end the bloodshed there.

And he took Iran to task for hosting a conference casting doubt on the Holocaust.

"The denial of the Holocaust is not acceptable," he said. "Nor is it acceptable to call for the elimination of any state or people," he added in reference to Iranian President Mahmoud Ahmadinejad's remarks that Israel should be "wiped off" the map and "would soon disappear".

He also said the deteriorating Middle East situation would be one of his priorities, particularly the need to settle the Israeli-Palestinian conflict.

He also urged Iran to resume negotiations with European powers to settle the standoff with the Security Council over its nuclear program "in a peaceful way".

On a lighter note, Ban flunked a French language test when he was was unable to answer a reporter's question posed in French as to why French should remain the second working language of the world body, after English.

After he fumbled a "je n'ai pas pu (I was not able)", an aide came to his rescue and translated the question into English, to which Ban replied that the decision to give priority to French was made by UN member states for reasons of "convenience and practicality."

By tradition, the UN secretary general is required to have a working knowledge of French.

Ban has been working assiduously on his French since he launched his bid to succeed Annan early this year. France's UN Ambassador Jean-Marc de La Sabliere certified that Ban's French was adequate.

Meanwhile the US acting Ambassador to the UN, Alejandro Wolff, whose country played a key role in Ban's appointment, said the South Korean "commands our full respect."

"We have full confidence in his ability, his goodwill and his desire to serve and to achieve," the US delegate said. "We look forward to working with the new secretary general and other member states to achieve our shared goal of making the United Nations stronger and more effective and thus further honor Kofi Annan's vision."

Earlier Thursday, the 192-member General Assembly paid a warm tribute to Annan, hailing his "exceptional contribution to international peace and security".

The assembly gave Annan a standing ovation and adopted by acclamation a resolution "acknowledging with deep gratitude" his "indefatigable efforts and dedicated service" over the past 10 years.

Ban has been at UN headquarters in New York since November working on setting up a transition team ahead of his official assumption of duties.

His election by the General Assembly last October was a mere formality after the powerful 15-member Security Council recommended him.

Ban will become the UN's eighth secretary general and the first Asian UN chief since U Thant of Burma led the organization from 1961 to 1971. He will lead a staff of over 15,000, drawn from more than 170 nations.