"We are challenging the qualifications of the candidate that was declared the winner. We are also challenging the processes that led to his declaration as the winner, among others," Labor Party spokesperson Yunusa Tanko told Reuters.
Obi, who campaigned as an outsider and galvanized young and first time voters, came third in the election, behind winner Bola Tinubu from the ruling All Progressives Congress party and main opposition People's Democratic Party's Atiku Abubakar.
Election observers from the European Union, the Commonwealth and other bodies reported a range of problems, among them failures in systems designed to prevent vote manipulation.
The observers criticised the electoral commission for poor planning and voting delays, but they did not allege fraud. The commission itself apologised for the technical problems during the count.
