Voters in Nigeria woke up Saturday morning to the news that the presidential and parliamentary elections have been postponed for a week.
Nigeria's election commission postponed the vote just hours before the polls were to open.
President Muhammadu Buhari called on Africa's most populous nation to remain calm. He said in a statement this is a "trying moment in our democratic journey."
The president said Nigeria's Independent National Electoral Commission (INEC) had "given assurances, day after day and almost hour after hour that they are in complete readiness for the elections." He added, "We and all our citizens believed them."
The chairman of Nigeria's Independent National Electoral Commission (INEC), Mahmood Yakubu, told reporters that "this was a difficult decision to take but necessary" for successful elections to take place.
He gave few details about why the change was made, but said "proceeding with the election as scheduled is no longer feasible."
Local media had reported that voting materials had not been delivered to all parts of the country.
An official of the election commission told Reuters news agency that "some result sheets and some ballot papers are reportedly missing."
?Close race expected
The Situation Room, a civic group monitoring the election, said the delay casts a "cloud of doubt" on INEC's credibility and competence.
Voters said they were confused and disappointed by the weeklong suspension after the electoral commission had said everything was in order.
"We are all surprised. No one is happy," said Usman Joe Yussuf, a business owner in Lagos.
The election is expected to be a tight race between incumbent President Buhari and his main challenger, former Vice President Atiku Abubakar.
Abubakar urged Nigerians to "come out and vote" next week and asked them to be "patient."
Nigerian authorities increased security across much of the country on Friday ahead of the anticipated elections.
Officials in Nigeria's Kaduna state Friday reported at least 66 deaths in a wave of violence. State officials said the victims included 22 children.
Kaduna is an area known for its ethnic tensions, Christian-Muslim violence and election-related unrest.
Hundreds of people were killed in the region in 2011 when then-opposition candidate Buhari, a Muslim former military ruler from the north, lost to Goodluck Jonathan, a Christian from the south.
President Buhari, 76, who beat Jonathan in a rematch in 2015, is running for re-election against main challenger Abubakar, a 72-year-old businessman and former vice president.
Along with ongoing violence in Kaduna, Nigeria is dealing with the decade-long Boko Haram Islamist insurgency in the northeast, and banditry and kidnappings in the northwest.
Before the announcement of a postponement, U.S. Secretary of State Mike Pompeo spoke with both President Buhari and Abubakar by phone on Friday, and "underscored U.S. support for the Nigerian goal of free, fair, transparent and peaceful elections."
Pompeo welcomed both candidates' pledges to accept the results of a credible election process and said the United States wants to see elections that reflect the will of the Nigerian people, according to a State Department statement.
Pompeo noted the "deep and long-standing partnership" between the United States and Nigeria, Africa's most-populous democracy and the continent's largest economy.