Nigeria's opposition says there are more than 1 million ghost voters on the national register head of Saturday's presidential election.
Uche Secondus, the chairman of the opposition People's Democratic Party, told a news conference in the capital, Abuja, on Thursday that the electoral commission "did not in fact do a cleanup of the register of voters" before publishing it.
He also alleged "a coordinated approach to register foreigners" as voters.
The People's Democratic Party, whose presidential candidate is Atiku Abubakar, is Nigeria's main opposition party.
A spokesman for the electoral commission did not respond to requests for a comment.
The electoral commission says 84 million people are registered to vote.
Nigerian President Muhammadu Buhari and his top challenger, Abubakar, renewed a pledge for a peaceful poll on Wednesday.