ABUJA, Nigeria — The leading presidential candidates in Nigeria urged their supporters to be patient on Saturday after officials said the election would be delayed by a week, just hours before the polls were to open.
In their 2:30 a.m. announcement of the postponement, election officials cited concerns about the logistics of delivering voting equipment. Millions of people, including President Muhammadu Buhari, had traveled long distances to their home districts to be in place to vote — Nigeria has no absentee voting system — and frustration was palpable.
The political parties of Mr. Buhari and his leading opponent, Atiku Abubakar, both condemned the decision, and each accused the other’s candidate of gaining an advantage from the delay.
The leaders of Mr. Buhari’s party said Mr. Abubakar would benefit from “a breather” and that his party had been “bent on discrediting this process the moment it realized it cannot make up the numbers to win this election.”
Mr. Abubakar’s party, for its part, accused the president of orchestrating the delay to suppress voter turnout. “Their plan is to provoke the public, hoping for a negative reaction, and then use that as an excuse for further antidemocratic acts,” the party said in a statement.
Yet both camps also urged supporters to be patient in the face of a delay that risks inflaming tensions in an already tense election.
The decision upended the plans of millions of people, including huge teams of international observers from the European Union, the African Union and pro-democracy organizations in the United States and elsewhere. Observers had fanned out across the country and set up command centers in hotel conference rooms for monitoring the election.
Voters vented on social media. Some said they had traveled to areas known for violence to cast their ballots, and that they were now stranded there without the election officials they had expected to rely on for security.
There were concerns that rumors and bogus news reports could spread about the reasons for the delay. And it seemed possible that still more logistical problems could develop.
Voting materials that have been delivered to polling stations may have to be returned to the capital, then redistributed before the new election date, Feb. 23, if officials decide not to leave them in place for security reasons. Several storage facilities where polling materials were being kept have already been burned.
Still, many experts and other observers were optimistic that a sense of calm would prevail. The past two Nigerian presidential elections were also delayed.
The campaign has been closely fought. More than 70 candidates will appear on ballots, but Mr. Buhari and Mr. Abubakar are by far the leading contenders.
The opposition has accused Mr. Buhari’s government of plotting to rig the elections. In turn, Abba Kyari, the president’s chief of staff, made a rare public comment in an article for an Nigerian newspaper, accusing the United States and the European Union of working with Mr. Abubakar’s party.
The governor of Kaduna, a close ally of Mr. Buhari, had earlier caused outrage by warning that foreign actors intervening in Nigeria would leave the country “in body bags.”
Critics of Mr. Buhari, 76, say that in four years in office he has failed to deliver on promises to fix the economy, tackle corruption and improve security. Attacks carried out by criminal organizations and by the terrorist group Boko Haram have been on the rise. This week, more than 60 people were killed in Kaduna in an attack blamed on religious tensions.
Critics also say the president has used his anticorruption campaign to target political enemies while sparing his allies.
Mr. Abubakar, 72, is a former vice president and wealthy businessman who has himself been dogged by accusations of corruption. In 2010, a United States Senate subcommittee accused him of funneling tens of millions of dollars’ worth of Nigerian oil revenues into foreign shell accounts. Mr. Abubakar has responded to the allegation by noting that he has never been charged with a crime.