Diallo won 39.72 percent of the vote, Conde took 20.67 percent, said the observer, Abdel-Fatau Musah.

That means Diallo and Conde will compete in a runoff for the presidency late this month or early next month, said Musah, who is political affairs director for the Economic Community of West African States.

Though the constitution calls for the runoff to be held July 18, "problems with preparations and things like that" will likely delay it until later in the month or early in August, he said.

Sunday's voting represented the first free ballot since the west African nation gained independence from France more than half a century ago. Observers applauded the vote in a country ruled by authoritarian and military dictators since it gained independence from France in 1958. About 77 percent of the 4 million people eligible to vote did so, he said.

Prior to Friday's announcement of the results, 21 of the candidates had accused the process of having been tainted by fraud, but Musah said observers found no widespread problems.