Nigeria's ruling party candidate Bola Tinubu was declared president-elect by the country's Independent National Electoral Commission (INEC) on Wednesday after a disputed weekend election.

Tinubu, 70, beat Atiku Abubakar, who ran on the ticket of the main opposition People's Democratic Party, and Peter Obi, a third-party candidate who has generated substantial buzz among young voters, in an election marred by allegations of fraud and manipulation in the vote-counting process.

Nigerian electoral law says a candidate can win just by getting more votes than their rivals, provided they get 25 percent of the vote in at least two-thirds of the 36 states and Abuja. 

Tinubu won the most ballots – 8.8 million – and crossed such thresholds in 29 states, according to the INEC. Atiku and Obi, who received 6.98 million and 6.06 million of the votes, respectively, came in second and third.

Opposition parties rejected the results as the product of a flawed process, which suffered multiple technical difficulties owing to the introduction of new technology by the INEC, and on Tuesday called on its chairman Mahmood Yakubu to resign.

The INEC has rejected the call, saying the procedures for aggrieved parties or candidates "do not include calling on the INEC chairman to resign or for the election to be cancelled."

Tinubu, the flagbearer of the All Progressives Congress (APC), a party he helped form with outgoing President Muhammadu Buhari in 2013, aims to continue incumbent administration policies including building public infrastructure and greater central bank intervention in the economy, but end a costly fuel subsidy and channel the money to agricultural and social welfare programs while expanding the military.

He forged his political career opposing military rule in the early 1990s. This is Tinubu's first presidential election run, which comes after years of forming political, ethnic and religious alliances across Nigeria. He is an ethnic Yoruba and a Muslim.

A Lagos governor between 1999 and 2007, Tinubu is an influential figure in the southwest, earning the nickname "Godfather of Lagos." During his two terms as governor, he managed to reduce violent crime, improve the city's traffic jams and clean up garbage.

His victory extends the APC's grip on power in Africa's top oil producer and most populous nation, though he inherits a litany of problems from Buhari.

Nigeria is struggling with Islamist insurgencies in the northeast, armed attacks, killings and kidnappings, conflict between livestock herders and farmers, cash, fuel and power shortages and perennial corruption that opponents say Buhari's party has failed to stamp out, despite promises to do so.

(With input from Reuters)