UNITED NATIONS — The coup that toppled Thailand’s prime minister complicates his deputy’s candidacy to be the next U.N. secretary-general, China’s U.N. ambassador said.

The race to succeed Secretary-General Annan, whose second five-year term ends December 31, is one of the hottest behind-the-scenes issues at the U.N. General Assembly.

Thai Deputy Prime Minister Surakiart was the first candidate to enter the race, and he won backing from the 10-member Association of Southeast Asian Nations at last year’s General Assembly ministerial meeting. Mr. Surakiart was in New York with Prime Minister Thaksin when the military launched a bloodless coup Tuesday. He flew to London with the former prime minister and was due back in Thailand yesterday.

“The interim government has already said that they continue to back Dr. Surakiart as the secretary-general,” the Thai Foreign Ministry’s deputy permanent secretary, Sihasak Phuangketkeow, said after a meeting on the sidelines of the General Assembly. But China’s U.N. Ambassador Wang Guangya said Wednesday, “I think definitely the situation in Thailand makes this issue more complicated.”

Traditionally, the United Nation’s top job rotates every 10 years by region.

Africa, in theory, should have handed over the secretary-general’s spacious office to Asia on January 1, 2002. But Mr. Annan was selected for a second term in 2001, in part because Asia could not agree on a candidate, giving Africa an unprecedented 15 years at the helm of the world body.

When Mr. Annan was elected, African, and Asian nations agreed that the next secretary-general should be Asian, though U.S. Ambassador John Bolton has said the job should go to the best-qualified candidate. There are currently seven candidates and more could emerge.

The newest, Afghanistan’s former finance minister Ashraf Ghani, officially entered the race on Wednesday when he was nominated by President Karzai.

The Afghan government said Mr. Ghani, the chancellor of Kabul University who spent 10 years working in China, India, and Russia for the World Bank, “is uniquely equipped” to lead the U.N.now, when imagination and leadership are needed to promote security and development.

In addition to Mr. Surakiart, he faces South Korean Foreign Minister Ban Kimoon; U.N. undersecretary-general for public affairs Shashi Tharoor of India; Jordan’s U.N.Ambassador Prince Zeid al Hussein; former U.N. disarmament chief Jayantha Dhanapala of Sri Lanka, and Latvian President Vaira Vike-Freiberga, the only non-Asian.

In an informal, secret poll of the 15 Security Council members on yesterday — before Vike-Freiberga entered the race — South Korea’s Ms. Ban came in first followed by India’s Mr. Tharoor. Mr. Surakiat was third, with Jordan’s Zeid fourth, and Mr. Dhanapala fifth. Thailand’s Mr. Sihasak said “ASEAN has indicated that they continue to back Surakiart as the new secretary-general.”

“I think the strength of Dr. Surakiart is first of all his qualifications. Second Thailand, our country, has always played a moderating role in international affairs, a bridge builder,” he said.