Nigeria's presidential candidate, Peter Obi, who lost a close election to the governing party's Bola Tinubu on February 25, announced Thursday that he would challenge the vote in court.

"We will explore all legal and peaceful options to reclaim our mandate. We won the election and we will prove it to Nigerians," the Labour Party candidate told journalists in the capital Abuja.

Obi received the third most votes, with 6.1 million, a major achievement for an outsider in a country dominated by two establishment parties.

Tinubu of the ruling All Progressives Congress (APC) was proclaimed winner on Wednesday with a total of 8.8 million votes and the required number of votes across two-thirds of Nigeria's states – a provision intended to ensure wide representation.

The former governor of Lagos will succeed President Muhammadu Buhari, who will leave office in May.

Atiku Abubakar of the opposition Peoples Democratic Party (PDP) received the second most votes, with 6.9 million.

Related News

Nigeria ruling party candidate Tinubu wins presidency

The elections in Africa's most populous country were mostly calm, but they were marred by long delays and the tardy release of online results, which irritated voters and opposition parties who claimed huge vote tampering.

"It will go down as one of the most controversial elections ever conducted in Nigeria," Obi said.

"The good and hardworking people of Nigeria have again been robbed by our supposed leaders whom they trusted," he added.

Nigerian elections have often been marked by fraud allegations and violence. 

Tinubu on Wednesday called on his rivals and their supporters to "join hands" with him, urging them to "come in so that we may begin the task of rebuilding our national home together."

Candidates who want to contest the election have 21 days after the results are announced to file a legal case.

Read next: Nigerians vote in tight race to choose successor to President Buhari