Nairobi/Accra - Ghana's electoral commission Tuesday evening refused to declare a winner in the West African nation's run-off presidential election, saying it would have to re-run one constituency in early January.

Partial results put John Atta Mills of the National Democratic Congress (NDC) on 50.13 per cent of the vote versus 49.87 per cent for Nana Akufo-Addo of the ruling New Patriotic Party (NPP) with 229 out of 230 constituencies counted.

Electoral commission chief Kwadwo Afari-Gyan said that the constituency of Tain would be re-run on Friday after polling was not completed there on Sunday.

He did explain what the problem was, although some reports said the constituency ran out of ballots.

Just 23,055 votes separate the two candidates in the run-off election, but the NDC won Tain in the inconclusive first round in early December.

Atta Mills scooped 16,211 votes to 14,935 for Akufo-Addo in Tain.

The results were supposed to be announced at 1200 GMT on Tuesday, but the two parties and the electoral commission instead spent hours locked in a meeting to try to resolve alleged irregularities.

Local media had projected a win for Atta Mills, who has already claimed victory.

Thousands of Atta Mills' supporters gathered outside the offices of the electoral commission Tuesday afternoon to demand that the commission officially declare their man the winner.

Banks of police backed up with water cannon stood by to deal with any possible trouble and shops and banks closed early as worries over possible violence grew, Ghanaian media reported.

The NDC has accused the NPP of attempting to tamper with results. Both sides have claimed their polling agents were intimidated and harassed and there were also reports of attempted ballot box theft.

US envoy to Africa Jendayi Frazer has called on both parties not to raise tensions by spreading rumours.

Outgoing President John Kufuor and former President John Rawlings on Tuesday also called for calm.

The election is seen as key to African democracy, which sorely needs a boost after electoral chaos in Kenya and Zimbabwe and coups in Mauritania and Guinea this year.

Foreign election monitoring teams were in place to observe the election.

The European Union's election monitoring team, which hailed the first round as a credit to democracy, said that the run-off was credible.

"Despite the heightened tensions and allegations by the political parties, the people of Ghana were able to cast their vote in an environment of transparency," EU Chief Observer Nickolay Mladenov said in a statement.

"Incidents of violence and attempts to disrupt polling were reported but they should not undermine the overall credibility of the election," Mladenov added.

Whoever wins the election will lead Ghana into the oil era.

Ghana's National Petroleum Corporation expects 120,000 barrels per day to come onstream in 2010, with that figure rising to 250,000 barrels a day within two years.

Ghana is the second-largest cocoa grower in the world and Africa's second-biggest gold producer, yet there is still widespread poverty among ordinary Ghanaians.

Both presidential candidates have promised good governance with the oil, to reduce poverty and to tackle rising food and fuel prices. (dpa)