Ghana's main opposition, alleging electoral fraud, filed a court challenge Friday to results from this month's presidential polls handing victory to incumbent John Dramani Mahama.
Opposition candidate Nana Akufo-Addo of the New Patriotic Party told journalists after the party filed the challenge with the supreme court that the discrepancies they are alleging were too large to ignore.
"The scale of what we have uncovered has surprised even the sceptical among us," he said. "Personally, it has been a sad experience."
He added later "we are ready to concede where there was more than 11 million voters there might be mistakes, but why are the arithmetic mistakes so often in favour of the NDC presidential candidate John Dramani Mahama?"
Akufo-Addo has refused to concede defeat in the December 7 election despite official results showing him with 47.7 percent against Mahama's 50.7 percent.
The NPP allegations involve some 1.3 million votes -- enough to tip the balance in favour of Akufo-Addo.
Observer groups have however hailed the conduct of the election, and an organisation of local monitors said the official figures roughly matched up with its findings.
Ghana was seeking to live up to its reputation as a beacon of democracy in west Africa in the presidential vote, its sixth since a return to civilian rule.
Ghana, west Africa's second-largest economy, is a major exporter of cocoa and gold and began producing oil in 2010.
Mahama, previously vice president, has been head of state only since July, following the death of his predecessor John Atta Mills.