Ghana's main opposition party is boycotting the swearing-in ceremony of President John Mahama following last month's disputed elections.

The New Patriotic Party (NPP) said Mr Mahama won the election fraudulently.

Official results gave Mr Mahama 50.7% of the vote, enough to avoid a run-off against the NPP's Nana Akufo-Addo, who won 47.7%.

Ahead of his inauguration, Mr Mahama called for unity in Ghana - seen as one of Africa's most stable democracies.

Mr Mahama was Ghana's vice-president until the unexpected death of President John Atta Mills in July.

He has served since then as acting president.

On Friday, Mr Mahama appealed to members of parliament to work together.

"For the long-term survival of our nation, we must agree and commit to a multi-partisan process," he said.

"Whatever our differences, whatever our politics, we must pull together and rise to meet these challenges."

Mr Mahama is due to be sworn in before 11 African heads of state, the BBC's Sammy Darko reports from the capital, Accra. Officials from the US, China and the UK will also be there.

The NPP filed a petition over the election result at the Supreme Court in late December, saying it had found irregularities including unregistered voters casting ballots.

Mr Mahama's National Democratic Congress (NDC) said the elections were the most transparent the country had seen.

International election observers described the 7 December poll as free and fair. Ghana's government says the presence of international leaders at Monday's ceremony is an endorsement of the vote.