Nigeria's main opposition party has rejected the result of a runoff for a governorship in the country's swing southwest after the ruling party narrowly won in a boost to President Muhammadu Buhari's re-election hopes.
Gboyega Oyetola of Buhari's All Progressives Congress (APC) was controversially declared winner of the Osun state poll by the Independent National Electoral Commission of Nigeria (INEC) late Thursday by a margin of fewer than 500 votes.
He won 255 505 votes compared to his closest challenger, Ademola Adeleke of the Peoples Democratic Party (PDP), who received 255 023.
The PDP rejected the final results, saying it's candidate was robbed of victory and vowed to challenge the decision in court.
An observer team from the EU, US and Britain called for "calm" and expressed concerns about alleged irregularities, harassment and interference in the vote.
"We are very concerned by these reports and will be checking stakeholders to check the facts," international observers said.
"We call on stakeholders to be calm."
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The vote in Osun was the final major test before Nigerians elect a new president, parliament, governors, and state legislatures in February and March next year.
The election was first held on Saturday, but was deadlocked when neither of the two leading candidates garnered the required number of votes for outright victory, according to the country's electoral law.
Following the rerun, INEC returning officer Professor Joseph Afuwape said: "Oyetola, having satisfied the requirement of the law, having scored the highest number of votes, is hereby declared the winner and he is returned elected."
Oyetola will take over from incumbent APC Governor Rauf Aregbesola, who is stepping down after two four-year terms, the legal maximum.
Economy and insecurity problems
Buhari on Friday congratulated the winner.
"President @MBuhari congratulates the All Progressives Congress (APC) and the Governor-elect of Osun State, Adegboyega Isiaka Oyetola, for winning the keenly contested governorship election," presidential spokesman Garba Shehu said on his Twitter handle.
Buhari, who became president in 2015, faces a formidable challenge from an array of opposition candidates from PDP, including former vice president Atiku Abubakar and Senate president Bukola Saraki, ahead of next year's key vote.
The 75-year-old retired general, who headed a military regime in the 1980s, is under pressure to step down because of failing health after spending several months in London last year treating an undisclosed ailment.
He has also come under fire over the management of the economy and growing insecurity problems, including Boko Haram insurgency in the northeast, long-running farmer-herder clashes in the centre and militancy and kidnapping in the south.