Ghana's main opposition party has announced plans to formally challenge the outcome of a presidential election won this month by incumbent Nana Akufo-Addo, a rare move in a country where losing candidates typically concede defeat.

Akufo-Addo was declared the winner of the December 7 vote with 51.59 percent, ahead of the opposition National Democratic Party's (NDC) candidate, former President John Mahama, who received 47.37 percent.

The contest witnessed heated rhetoric during campaigning and election-related violence that killed at least five people, a rarity in a country that has a reputation as one of West Africa's most stable democracies.

"The NDC will contest the results of the rigged election in the Supreme Court and other appropriate fora," the party's executive committee said in a statement on Tuesday.

The NDC, which has yet to produce evidence of fraud, provided no details about the case it would file. The court has 42 working days from when hearings begin to issue its decision.

Only one other Ghanaian presidential election, in 2012, was formally contested by the losing candidate.

The court rejected Akufo-Addo's challenge to then-incumbent Mahama's victory in a case that dragged on for eight months.

(With input from agencies)