Syria said it would pursue its bid for a seat on the UN nuclear watchdog's governing body despite US-led opposition to Damascus, which is under investigation for alleged covert atomic work.

The International Atomic Energy Agency (IAEA) has been investigating Syria since May over US intelligence allegations that it almost built a secret, plutonium-producing reactor before Israel destroyed the site in an air strike a year ago.

Damascus has denied having a secret nuclear programme and the IAEA said last week preliminary findings from an inspectors' visit to the site in June showed no evidence of one.

Syria is competing with US ally Afghanistan for the nomination to a seat on the IAEA's 35-country Board of Governors reserved for a representative of the Middle East and South Asian group in the IAEA's assembly of 145 member states.

Known as Mesa, the group must agree on one candidate by consensus to win automatic approval by the assembly, whose annual General Conference opened in Vienna on Monday.

Arab diplomats said Afghanistan was clinging to its candidacy with US encouragement, despite scant support within Mesa, while Syria had broad backing within the group, where fellow Arab League countries predominate.

If Mesa cannot settle on a single candidate, the assembly will hold a vote later this week on both candidates, unprecedented and highly divisive in a body that prides itself on consensus. The winner would be chosen by a simple majority.

Mohammad Badi Khattab, Syria's ambassador to the IAEA, said Damascus saw no reason to drop out because it had official Arab League support and Afghanistan was isolated in Mesa.

"The matter is not yet settled. Syria and Afghanistan are still in the race. But nobody in Mesa backs Afghanistan, they are alone," Khattab told Reuters.

Afghanistan's IAEA envoy told Reuters Kabul would not back out because it could count on majority backing in the assembly.

"We are the better candidate. We'll represent Islamic interests and improve understanding between the Islamic world and the West, and being on the board will contribute to the progress of democracy in Afghanistan," said Wahid Monawar.

A senior Western diplomat said consultations showed some 89 members of the assembly would oppose Syria in a vote, including all European Union members, Japan, Canada, Australia and some African, Asian and Latin American states.

The diplomat said Syria's backing in Mesa was not as solid as it seemed and that some in the group would turn against Damascus in a secret ballot. "Some who back Syria publicly won't do it privately."

A second Western diplomat said: "A matter of principle is at stake here - we can't have countries on this (policy-making) board who are not IAEA members in good standing."

Arab diplomats said Syria was unlikely to back out because its candidacy was endorsed at an Arab League summit in March.

"The Americans lobbied almost every other Arab country that was not on the board, mainly (pro-Western) Gulf countries, to go for the seat but failed," one Arab diplomat said.

"Why block Syria? There is no proven proliferation problem there. Libya was on the board for a year recently even though it remained under IAEA investigation."

Libya renounced an illicit atomic bomb programme in 2003 and an IAEA report this month certified that the North African state had indeed eliminated its nuclear weapons capacity.-Reuters