The opposition candidate in Ghana's presidential run-off has a narrow lead over the ruling party candidate in the early vote count.
Media reports Monday say John Atta-Mills of the opposition National Democratic Congress is running a close race with Nana Akufo-Addo of the ruling New Patriotic Party.
However, both parties say their supporters were subjected to intimidation tactics at the polls.
The U.S. assistant secretary of state for Africa, Jendayi Frazer, says the United States considers Ghana a model of democracy and that both parties must behave responsibly.
The winner of Sunday's runoff will replace President John Kufuor, who is stepping down after eight years in power.
Akufo-Addo is promising to continue the economic policies of President Kufuor.
Opposition candidate Atta-Mills says it is time for change. He says that despite the country's economic growth, many Ghanaians have little to show for the progress.
Ghana is a major producer of gold and cocoa and plans to start pumping oil from last year's offshore discovery by 2010.
But despite Ghana's wealth of natural resources, many Ghanaians live in poverty.
Some information for this report was provided by AFP and Reuters.