The United States called Thursday on all sides in Nigeria including the military to ensure that next week's election is "free from outside pressure and intimidation."
Amid mounting tensions over potential violence and vote-rigging, Secretary of State Mike Pompeo said the February 16 vote offered "an opportunity for Nigeria to solidify its place as a democratic leader in Africa."
"The United States government supports a free, fair, transparent and peaceful election that reflects the will of the Nigerian people," Pompeo said in a statement.
"Nigerian security services must provide a safe and secure environment for the Nigerian people to exercise their rights. Those who interfere in the electoral process or incite violence must be held to account," he said.
Fraud accusations and violence have marred elections since civilian rule was restored in 1999 in Africa's most populous country, although observers say the last vote in 2015 that elected President Muhammadu Buhari were generally fair.
Buhari is running for a second term against former vice president Atiku Abubakar, whose main opposition party has accused the ruling forces of trying to rig the vote.
Buhari's All Progressives Congress has in turn accused the opposition of fomenting unrest.
Defense spokesman John Agim earlier Thursday promised that the military would remain neutral in the election.
The United States has built political and economic relations with Nigeria since the restoration of democracy and in recent years has been especially involved in supporting its fight against Boko Haram extremists.