The U.S. government has congratulated President Muhammadu Buhari on his re-election.
Mr Buhari of the All Progressives Congress defeated Atiku Abubakar of the Peoples Democratic Party to win the presidential election.
Mr Abubakar and the PDP have, however, alleged fraud and vowed to challenge the result in court.
In its statement by Michael Pompeo, the Secretary of State, the U.S. said it "congratulates the people of Nigeria on a successful presidential election, and President Muhammadu Buhari on his re-election."
"We commend all those Nigerians who participated peacefully in the election and condemn those whose acts of violence harmed Nigerians and the electoral process.
"We note the assessments of international and domestic observer missions affirming the overall credibility of the election, despite localized violence and irregularities.
"We also congratulate all the other candidates for their peaceful participation in the electoral process. We call on all Nigerians to ensure successful state elections next week.
"Going forward, the United States remains committed to working together with Nigeria to achieve greater peace and prosperity for both our nations."