Nairobi/Accra - Polls closed Friday evening in the last Ghanaian constituency to cast its ballots in a run-off presidential election that has become increasingly tinged with controversy.

The remote farming constituency of Tain, which has just over 53,000 registered voters, could not complete its vote in Sunday's presidential run-off election after problems distributing the ballots.

John Atta Mills of the opposition National Democratic Congress (NDC) holds a 23,055-vote lead over Nana Akufo-Addo of the ruling New Patriotic Party (NPP), meaning that the constituency has the power to decide who wins.

Atta Mills won Tain in the inconclusive first round in early December with 16,211 votes to 14,935 for Akufo-Addo.

The NPP, staring defeat in the face, on Thursday brought two court cases in an attempt to turn its fortunes around.

The first case was aimed at stopping the electoral commission from announcing the results until the NPP's allegations of fraud in the NCD Stronghold of Volta were addressed. The court refused to hear the case.

The NPP then sought an injunction preventing the voting in Tain from going ahead, saying conditions for a free and fair election did not exist in the constituency.

NPP polling agents boycotted the vote, although it was not clear how many of their voters followed suit.

Electoral Commission Chairman Kwadwo Afari-Gyan will announce the result at 1100 GMT Saturday, Ghanaian radio station Joy FM reported.

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 last year.

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

Other observers, including US envoy to Africa Jendayi Frazer, have called on both parties not to raise tensions by spreading rumours.

Both parties have levelled accusations of fraud, harassment and intimidation.

Tensions have been high among the party supporters. Police had to cordon off the electoral commission's offices on Tuesday as NDC supporters demanded the result be called in favour of Atta Mills.

Religious and civil society leaders in Ghana have this week repeatedly called on both parties to accept the final outcome of the election to save the nation from conflict.

Outgoing president John Kufuor added his voice to the calls for accept the authority of the election commission and settle any appeals through "due process" later on.

Ghana, like Kenya before the post-election violence that followed the December 2007 presidential elections, is considered one of Africa's few truly functioning democracies.

The West African nation underwent coups in the 1970s and 1980s, but coup leader Jerry Rawlings organized elections and went on to win two terms.

He then handed over power to Kufuor in 2000 when his party's candidate - Atta Mills in his first attempt at the presidency - lost.

Ghana has thus managed several peaceful handovers of power, but this time around the stakes are particularly high as 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 after Ivory Coast and Africa's second-biggest gold producer after South Africa, 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)