Nigeria's ruling party candidate Bola Tinubu won the country's highly disputed weekend election Wednesday.

The win secures the former Lagos governor his life-long ambition of the presidency of Africa's most populous democracy.

The president-elect defended Wednesday the integrity of the national election and called on citizens to unite around him after a bitter dispute over results opposition parties have said are flawed.

The Independent National Electoral Commission (INEC) said Tinubu garnered 8.79 million votes in the weekend election, ahead of main opposition challenger Atiku Abubakar's 6.98 million votes.

Peter Obi, an outsider popular with younger and more educated urban voters, garnered 6.1 million votes.

A candidate can win a Nigerian election by getting more votes than their rivals, provided they get 25% of the vote in at least two-thirds of the 36 states and the federal capital Abuja, which Tinubu did.

"I am very happy I have been elected the president of the federal republic of Nigeria," Tinubu said to cheers in Abuja. "This is a serious mandate. I hereby accept it."

Nigeria's election was meant to be its fairest and most open contest to date. But the electoral process encountered problems, owing to new technology that did not function well and seemed to overwhelm Nigeria's notoriously inadequate communications network.

INEC had promised to upload results from each polling unit to its website in real time but most units were unable to do so immediately, undermining trust in the process. Thousands of results have still to be uploaded.

Because of these failings, the main opposition parties of Atiku and Obi have rejected the results as fraudulent.

"I commend INEC for running a credible election no matter what anybody says," Tinubu said. "The lapses that were reported, they were relatively few in number and were immaterial to affect the final outcome of the election."

Tinubu now faces a long list of national problems including Islamist insurgencies in the northeast, armed attacks, killings and kidnappings, conflict between livestock herders and farmers, cash, fuel and power shortages, and deeply entrenched corruption.