U.N. nuclear watchdog governors failed to agree on a successor to Director-General Mohamed ElBaradei on Friday after five rounds of voting, opening the field to new candidates who might bridge rich-poor divisions.

The International Atomic Energy Agency was keen to avoid a long delay installing a new chief as it confronts mounting challenges, including Iran's disputed pursuit of nuclear technology that could yield atomic bombs and a shortage of financial means to uphold the IAEA's anti-proliferation mandate.

Yukiya Amano, Japan's ambassador to the IAEA, was the leading candidate but fell a single vote short of the two-thirds majority required in the two-day election at a special session of the IAEA's 35-nation Board of Governors.

There were three inconclusive rounds on Thursday in which Amano, 61, outpolled South Africa's IAEA governor, Abdul Samad Minty, 69, in a competitive ballot, but not by a winning margin.

On Friday, the board resorted to two runoff, yes, no or abstain ballots for each candidate. Amano took 22 yes votes, 12 no with one abstention. Minty garnered 15 yes votes, 19 no with one abstention.

All votes split largely along rich and poor nation lines. Industrialized states backed Amano, developing states Minty.

The slate of candidates is considered to have been wiped clean, Ambassador Taous Feroukhi of Algeria, chairman of the Vienna-based governing board, told reporters.

New contenders -- including several Latin Americans who may be waiting in the wings -- will have 28 days from Monday to throw their hats in the ring, followed by another closed-door governors' ballot in May.

A Japanese foreign ministry official told Japanese journalists Amano would re-enter the race. Minty said he would have consultations with supporters before deciding what to do.

ELUSIVE CONSENSUS CANDIDATE

Feroukhi said both Amano and Minty had strong credentials, but told Reuters: A consensus candidate (is needed), someone who doesn't mark out clear differences like this ... between the developed and developing countries. Someone for both.

The IAEA's mandate is a politically tricky balancing act -- to catch secret nuclear bomb programs and to coordinate global cooperation in sharing nuclear energy for peaceful purposes.

Diplomats said Amano and Minty failed to convince many that they could bridge disputes between industrialized member states that already have nuclear energy and developing nations pressing for a share of it despite concerns about proliferation risks.

Minty voiced bitterness at Friday's outcome. We were hopeful that those that advocated change and a relationship with the developing world based on trust and partnership would -- in this important election process -- have implemented these noble ideals, but sadly it appears as this has only remained as good intentions, he said in a statement to governors.

With around half-a-dozen compromise candidates waiting in the wings, Feroukhi planned consultations to see if a consensus might emerge for one candidate, in keeping with multilateral tradition and to avoid internal IAEA divisions later.

Possible fresh nominees included:

* Luis Echavarri, Spanish director of the Organization for Economic Cooperation and Development's nuclear energy agency.

* Rogelio Pfirter, Argentinean head of the Organization for the Prohibition of Chemical Weapons in The Hague and a seasoned former nuclear treaty negotiator.

* Milenko Skoknic, Chile's ambassador to the IAEA and Feroukhi's predecessor as board chairman.

ElBaradei, who shared the Nobel peace prize with his agency in 2005, leaves office in November after 12 years, recently marked by spats with the Bush administration over what he saw as its warlike approach to resolving Iran's nuclear issue.

IAEA officials hope a change in U.S. foreign policy under President Barack Obama might shore up their efforts to prevent the stealthy spread of nuclear weapons technology.

Obama has signaled readiness to talk without preconditions with Iran and Syria, both subject to IAEA investigations now at an impasse, and eventually double what ElBaradei has called a shoestring IAEA budget not up to tackling challenges ahead.

Japan Algeria South Africa