By Kwasi Kpodo and Richard Valdmanis
ACCRA (Reuters) - Newly elected Ghanaian President John Dramani Mahama on Monday urged his defeated political opponents to join him "as partners" to improve the West African state, as his chief rival threatened to launch a court battle over the poll results.
Mahama was declared winner of the December 7 election, which was widely seen as a test of whether country - one of the fastest growing economies in Africa - can maintain its reputation as a pillar of democracy in a troubled region.
"I wish to welcome my fellow candidates to join me now as partners in the projects of nation-building and of creating a better Ghana," Mahama said in a victory speech to cheering crowds at a field in the capital Accra.
"We have come too far on this journey to weigh ourselves down with pettiness, intolerance and negativity."
Ghana's electoral commission said on Sunday Mahama, who replaced former president John Atta Mills after his death in July, had won 50.7 percent of the ballots cast, enough to avoid a run-off against his main rival Nana Akufo-Addo.
The West African nation's non-partisan Coalition of Domestic Election Observers (CODEO), which deployed more than 4,000 poll watchers, said the vote had been generally free and fair.
But Akufo-Addo said on Monday his party would take a decision on Tuesday on whether to challenge the results, which he said were manipulated by electoral workers.
"We have serious reservations about the counting and the declaration of results," Akufo-Addo told Reuters in his office at his residence in Accra.
"If we are going to challenge the results, the main question is; do we have enough evidence to suggest that, materially, the evidence will have affected the outcome?"
"The obvious option is to go and challenge the results in the courts. The other option is to forego it and make your case to the country," Akufo-Addo said.
Akufo-Addo called for calm among his supporters, saying leaders of his conservative-leaning New Patriotic Party would meet on Tuesday to decide the party's response.
On the wall of his office is a portrait of his father Edward Akufo-Addo, president from August 1970 to January 1972 before he was deposed by a military coup. Outside, there was a dour atmosphere among supporters milling about the yard, some yelling that the election had been stolen.
A cliff-hanger election in 2008, in which Akufo-Addo lost by less than 1 percent, pushed the country to the brink of chaos, with disputes over results driving hundreds of people into the streets with clubs and machetes.
Ghana's sprawling seaside capital Accra was bustling as normal on Monday.
The cocoa and gold-producing nation, which also began pumping oil in 2010, has had five peaceful and constitutional transfers of power since its last coup in 1981.
Voting on Friday was fraught with delays after hundreds of newly introduced electronic fingerprint readers failed, forcing some polling stations to reopen on Saturday to clear the backlog.
But CODEO observers said their parallel tabulation of results confirmed those declared by the electoral commission.
"The results of the 2012 presidential polls declared by the Electoral Commission are generally an accurate reflection of how Ghanaians voted in the December 7 polls," the group said in a statement.
The African Union's current chairman, Benin President Thomas Yayi Boni, visited Accra on Monday and congratulated Mahama on his win.
(Writing by Bate Felix and Richard Valdmanis; Editing by David Lewis and Myra MacDonald)