United Nations chief Ban Ki-moon is calling on candidates in Gabon to refrain from claiming victory in Saturday's presidential election until the results are released.
Sunday, presidential challenger Jean Ping said early results indicate he has won the vote, while a spokesman for incumbent Ali Bongo said the president is headed to a second term.
Gabon does not have a run-off system, so the candidate with the most votes in the 10-candidate field will win.
A victory by former African Union leader Ping would end a half-century of Bongo family rule. Ali Bongo succeeded his father Omar Bongo who died in 2009 after more than four decades in office.
Monday, the secretary-general congratulated Gabon for a peaceful election and said he hopes that peace will prevail before and after announcement of the provisional results, which are expected Tuesday.
Ban said it is important for everyone "to abide by the electoral law and refrain from making remarks on the outcome of the election before it is known."
Both sides accuse the other of fraud in the voting.
President Bongo's spokesman said "massive fraud" had been observed, particularly at polling stations in opposition territory.