Nigeria's president is vowing "safety and full protection" for foreign election observers, diplomats and others as Africa's most populous country goes to the polls on Saturday.
President Muhammadu Buhari's government has been under pressure over recent comments criticizing so-called foreign interference in the vote.
While the previous election was one of the most peaceful in Nigeria's history, others have been marred by deadly violence along religious and regional lines.
Buhari in his nationally televised address Thursday night urged Nigerians not to let differences "drive us to desperation" and urged youth to not let themselves be used for violence.
He seeks a second four-year term on Saturday.
Nigeria's leader says he has assured former U.S. President Bill Clinton of his commitment to "free, fair and credible elections" on Saturday and beyond.
A statement by President Muhammadu Buhari's office says the two leaders spoke by phone on Wednesday night after Clinton was not able to come to Nigeria and witness the signing of a peace accord by presidential candidates. The candidates pledged to contribute to an election free of the violence that has often followed past votes.
The statement says Clinton wished Nigeria well as Africa's most populous country, with 190 million people, goes to the polls. The previous vote in 2015 has been described as one of the most peaceful in the country's history.
There has been some tension over what some Nigerian officials have called foreign interference in this election, notably after the U.S., the UK and European Union expressed concern over Buhari's recent suspension of the country's Chief Justice.
SITE Intelligence Group says the Islamic State's West Africa Province has claimed responsibility for an attack on a convoy carrying a Nigerian governor in the country's northeastern Borno state, which occurred days before the country's elections.
The U.S.-based monitoring group says that IS West Africa Province released a statement Wednesday saying the attack on Kashim Shettima's convoy, and clashes with security forces killed 42 people. However, the government of Borno State said Thursday that only three people were killed.
The IS West Africa Province is a splinter group from the Nigeria-based jihadist group Boko Haram.
A member of a local defense group, who spoke on anonymity for security reasons, said some of the attackers were dressed as soldiers when they ambushed the convoy near Dikwa.
He said two civilians and a soldier were killed and the attackers left with eight vehicles and some hostages.
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.