The board of governors of the International Atomic Energy Agency is set to meet for a formal vote on the successor to Mohamed El Baradei, the head of the agency.

Yukiya Amano, the Japanese IAEA ambassador, remains favourite for Thursday's meeting, but diplomats have said there is still no sign of a consensus candidate.

"I see a deadlock as the most likely [outcome], unless Amano can pull something very big out of the hat," an EU diplomat said.

Amano fell a single vote short of the 24 needed at the first election in March, but his backing slid to 20 in a recent test poll.

Russia has told other board members that it will be "unacceptable" if Amano is elected by only the minimum winning margin, another EU diplomat said.

Rich-poor split

Such an outcome would harden a North-South split undermining the next IAEA chief's authority, he added.

El Baradei, an Egyptian diplomat, has been in the job for 12 years and served three terms and will be stepping down as director-general in November.

His successor will assume the highly sensitive nuclear dossiers of Syria, Iran and North Korea and will also have to persuade IAEA member countries to contribute more money to its budget.

The race to replace him narrowed when Jean-Pol Poncelet, a former Belgian deputy prime minister and now an executive at Areva, the French nuclear group, withdrew his name.

Poncelet finished last in a June 9 straw poll among five men, along with Slovenia's Ernest Petric, who on Tuesday dropped out of the race.

Past votes on the IAEA's 35-nation governing board have split along divisions between rich and poor nations.

El Baradei, who won the the Nobel Peace Prize in 2005 for his work at the IAEA, has often been criticised as being too outspoken and has also been accused of politicising the agency.