By Kwasi Kpodo
ACCRA (Reuters) - Ghana's opposition leader John Atta Mills was declared the winner of a closely fought presidential election run-off on Saturday, sweeping his party back to power after eight years.
The poll raised tensions in the gold and cocoa exporting country and challenges by both main parties had threatened to mar an election seen as a chance to bolster Africa's democratic credentials after flawed ballots elsewhere.
Results of voting in a final constituency on Friday showed Mills, of the National Democratic Congress (NDC), narrowly defeated Nana Akufo-Addo of the New Patriotic Party (NPP), which lost its parliamentary majority in an election last month.
Mills, winning his third bid for the presidency after losing twice to outgoing NPP President John Kufuor, was conciliatory.
"I want to assure everybody that I will be president for all. There will be no discrimination," Mills said in a victory speech to thousands of NDC supporters who thronged the streets around his office in the capital Accra.
"I would want to congratulate all other contestants, especially Nana Akufo-Addo, for giving us a good fight. It is my hope that we will be able to work together to build a better Ghana," he said. Then an aide popped open a bottle of champagne.
Akufo-Addo conceded defeat.
"I acknowledge the electoral commissioner's declaration and congratulate Professor Mills," he told a news conference. Outside, crowds of angry NPP supporters threatened journalists, who had to be escorted inside by party staff.
International monitors say voting has been mostly peaceful.
The West African country's political stability has attracted growing numbers of foreign investors as it prepares to produce oil in late 2010.
Announcing the results in the capital Accra, Electoral Commission Chairman Kwadwo Afari-Gyan said Mills won 50.23 percent overall against 49.77 percent for Akufo-Addo.
Neither candidate won a majority in the original December 7 poll and run-off voting in all but one of 230 constituencies last Sunday was inconclusive, so the election was decided by Friday's voting in the rural constituency of Tain.
FROM RULING PARTY TO LOSING PARTY
The NPP, which lost its parliamentary majority in the election but remains in power until President Kufuor steps down on January 7, boycotted the Tain vote over security concerns but failed to prevent the poll taking place.
Kufuor served the maximum two terms he is allowed.
Outside Mills's office, a woman dragged an effigy of an elephant -- the NPP's campaign mascot -- in a mock funeral as other NDC supporters chanted "Elephants, go back to the bush!."
"You have cause to celebrate, but let's not do anything to provoke disunity. We must know that this is only one day in a journey of a million miles," Mills told his supporters.
Each side has accused the other's activists of violence and irregularities and appealed to the electoral commission to review some of the results from last Sunday's vote.
Afari-Gyan said the commission had found no evidence to call the results into question and declared Mills president-elect.
The centre-left NDC has promised change after eight years of NPP rule, though analysts say there are few policy differences.
"Essentially, Ghanaians have said the two key political parties must work together. There are still some problems that need solving ... We want our politicians to work together to resolve them," Abena Amoah, head of investment banking and financing at Renaissance Capital's Ghana branch, told Reuters.
Kufuor won power when Mills's NDC ally, former coup leader Jerry Rawlings, stepped down in early 2000 after two terms.
Kufuor's pro-market rule has seen Ghana's economy become one of the most attractive investment destinations in the region.
But critics say his administration has failed to tackle widespread corruption, including drug smuggling.
