The International Atomic Energy Agency (IAEA) on Thursday failed to elect a new chief after three rounds of voting.
Neither of the two candidates, Japan's Yukiya Amano and South Africa's Abdul Samad Minty, managed to win the two-thirds majority needed to become the next IAEA director-general and succeed Mohamed ElBaradei.
New rounds of voting were expected on Friday.
Under the IAEA statutes, the agency's Board of Governors appoint the chief with the approval of the general conference of member states. ElBaradei will complete his term in November and the board has to elect a successor.
Nominations for the post have come from Japan, which has nominated 61-year-old diplomat Yukiya Amano, and South Africa, which nominated 69-year-old envoy Abdul Samad Minty.
Amano secured 21 votes in the first round of secret balloting, while Minty bagged 14.
In the second round, Amano's votes fell to 20, while Minty got 15. The third round repeated the former voting.
If neither of the hopefuls secures a victory after five rounds, new candidates can be nominated.
The two candidates have worked for the agency for many years, with excellent experience in the disarmament field.
It was difficult to have the consensus, as Westerners mostly supported Amano, while members from the developing countries preferred Minty.
Western countries apparently do not want to have another outspoken chief like ElBaradei. Instead, they hoped that the next leader would "not be so political".
They also suggested that since ElBaradei is an Egyptian, in accordance with the principles of balance, his successor should not come from Africa.