Election monitors in Ghana are investigating claims of fraud as votes in the closely-fought presidential run-off poll continue to be counted. Supporters of Nana Akufo-Addo, of the governing party, and the opposition's John Atta Mills claim the other side committed vote fraud and intimidation. Mr Addo defeated his rival by a slender margin in the first round on 7 December but not by enough to avoid the run-off. Both men hope to succeed President John Kufuor, who has served two terms. The stakes are high as Ghana has just found commercial quantities of oil. The two main political parties - the governing New Patriotic Party (NPP) and the National Democratic Congress (NDC) of Mr Atta Mills - both complained about apparent efforts to rig the vote. Ghana has held successful elections before but suspicions are high and there is a danger that, unless the people believe this process is free and fair, the country's image could be dented, says the BBC's Will Ross in Accra. Some 12.5 million people were eligible to vote in the election - the third since the country's return to democracy in 1992. 'Intimidation scheme' The US envoy to Africa, Jendayi Frazer, urged both parties not to spread rumours. "Some of the statements by the political parties' officials have been irresponsible and there are a number of rumours that have been going on that are being repeated by some of the radio stations that are associated with the parties," she said. In Accra and across the West African state, queues formed outside schools and other public buildings where polling stations were operating, guarded by armed soldiers and police. Mr Addo, who won the first round with 49% of the vote, said he was confident of winning the second. Election candidates John Attah Mills (left) and Nana Akufo-Addo (composite image) A big oil discovery has raised the stakes for the race "My chances are bright. I won the first round, as you know, and in principle I will be the leader in the second round. "What is important is for the Ghanaian people to make their choice in peace, and in tranquillity," he said. After Mr Atta-Mills cast his ballot in the capital, he said he hoped the voting would be smooth and carried out properly. "We don't want any rigging, we don't want any cheating," he said, adding that he was "confident of winning". On the eve of Sunday's vote, Mr Atta Mills said he had received disturbing reports of "macho men" being hired "to cause mayhem at polling stations". Mr Akufo-Addo's party accused the opposition of having embarked on a "disturbing... intimidation scheme". President Kufuor, who has to stand down having served two consecutive terms, urged Ghanaians to "keep cool" and vote "as a peaceful exercise, as a legitimate exercise". Ghana, traditionally an exporter of cocoa and gold, is preparing to start producing oil in commercial quantities from late 2010 and a major boost to the economy is anticipated. Source: BBC