Accra - The opposition candidate in Ghana's presidential polls said he is not ready to concede defeat after alleging a "pattern of fraud", but has not yet decided whether to challenge the results in court.
Nana Akufo-Addo, a 68-year-old human rights lawyer, made the comments on Monday after his party alleged irregularities in the election won by incumbent John Dramani Mahama, as the country seeks to maintain its reputation as a model African democracy.
"For me, the image of Ghana shouldn't be a falsehood," Akufo-Addo told reporters at his home.
"It shouldn't be that on the surface we have democracy, but underneath we have something else. We want the democracy of Ghana to be a genuine one."
The son of a former president said "there would seem to be a serious case for saying something seriously went wrong", but added that the party was continuing to investigate and would decide how to proceed. He expected a decision in the coming days.
A crowd of loyalists had gathered outside Akufo-Addo's house in support for the candidate, who lost 2008 elections by less than one percentage point.
President Mahama received welcome support from Washington on Monday as the White House urged all Ghanaians to accept the result of their election and congratulated him on his victory.
According to the electoral commission, Mahama won the election held over Friday and Saturday with 50.70% of the votes cast, compared to Akufo-Addo's 47.74%.
Observers from the Commonwealth, West African bloc Ecowas and local group CODEO - which deployed election observers - all said the vote appeared peaceful and transparent but Akufo-Addo said on Monday he was not ready to admit defeat.
"The United States congratulates President John Dramani Mahama and the people of Ghana for the successful election on December 7," White House press secretary Jay Carney said in a statement.
"The United States encourages all parties to accept the results and to use the appropriate legal processes to resolve any electoral disputes."
Late in the afternoon, Benin's President Thomas Boni Yayi, also the current head of the African Union, visited Akufo-Addo's home and the two had a brief conversation with reporters in the room, but their discussions could not be heard.
When the gates opened for Yayi's convoy to enter Akufo-Addo's compound, dozens of supporters streamed through with some approaching his front door to shout encouragement at their party's leader.
The stakes are especially high in the West African country with a booming economy fuelled in part by a new and expanding oil industry.
Addressing a celebratory crowd of supporters in the central Accra on Monday, Mahama sought to move the country past the "hard fought campaign".
"I wish to welcome my fellow candidates to join me now as partners in ... creating a better Ghana," he said, after previously calling on his rivals to respect "the voice of the people".
The opposition however issued a scathing statement even before the official results were announced.
"Indeed, we have enough concrete evidence to show that the 2012 presidential election was won by our candidate, Nana Akufo-Addo," it said, alleging a "pattern of fraud".
In the wake of the opposition claims and before the results were announced Sunday, a crowd of about 300 NPP supporters had gathered near the electoral commission. Security forces fired tear gas at one point in an apparent bid to move them back.
The 54-year-old Mahama, previously vice president, has only been head of state since July, following the death of his predecessor John Atta Mills.
Elections since the return to civilian rule in 1992 have seen both parties voted out of office, establishing Ghana's democratic credentials in a region that has had its share of rigged polls and coups.
Ghana is also a top exporter of cocoa and gold, with economic growth of 14% in 2011. Eight percent growth is expected this year and next in the country of some 24 million people.