Opposition leaders in Cameroon are demanding a nullification of Sunday's presidential election.

The vice chairman of the Social Democratic Front says the election was a “complete mess” and that its winner should not be given “any legitimacy.” He says his party intends to file a formal complaint to the country's supreme court on Wednesday.

The SDF's leader, John Fru Ndi, was widely seen as President Paul Biya's main challenger, although Mr. Biya's re-election never seemed to be in doubt.

Election observers said turnout was extremely low on Sunday, with many Cameroonians expressing apathy, saying the winner was already decided. Mr. Biya is widely expected to win a new seven-year term, extending his 29-year rule over the central African state.

The opposition accuses Cameroon's electoral commission of favoring the ruling party, and there have been complaints about irregularities on voter lists.

On Tuesday, United Nations Secretary General Ban Ki-moon said he welcomes the “peaceful manner” in which the presidential election took place, appealing to all political actors to “use established legal channels to resolve electoral disputes.”

Cameroon's former colonial power France said it saw no irregularities with the election, saying it had been held in “acceptable conditions.”

While President Biya admitted on Sunday that there may be “imperfections” in the voting process, he pleaded for patience, saying his government has no intention of cheating.

Official elections results may not be released for two weeks, but observers said polling stations were conspicuously uncrowded on Sunday, with some reporting fewer than 15% of registered voters turning up.

The 78-year-old leader has ruled Cameroon since 1982. In 2008 he eliminated constitutionally mandated term limits so he could run for re-election this year. That move sparked street protests in which at least 40 people were killed.