The White House issued a statement congratulating Mahama on winning election hailing the country for its peaceful votes.
Jake Obetsebi Lamptey, a spokesman for the opposition New Patriotic Party, told the BBC, however, the votes were manipulated in favor of Mahama. The results indicate Mahama won 50.7 percent of the vote, though the NPP spokesman said there was "robust" evidence of vote tampering.
The White House said it encouraged political parties in Ghana to accept the results of the election and use legal means to air grievances. African election observers described the presidential and parliamentary vote as free and fair.
Ghana is considered a model for African democracy. Its economy has been supported by recent oil discoveries.