Nigerians—millions of whom have traveled long distances to vote in their home region—awoke to the news early Saturday with a mixture of bafflement and anger. Nigeria postponed the 2015 presidential vote for six weeks because of rampant insecurity across the northeast, a region still bedeviled by jihadist violence.

“People have come from across the country, outside the country even from the U.S.,” said Asabe Anwar, a student who had returned to the northeastern city of Yola, to cast her first election vote. …

The delay is creating an information vacuum, which is already being filled by rumors, allegations and conspiracy. Supporters from both parties took to social media to claim that dark forces were plotting to rig the elections. …

Some 84 million people are registered to vote in the election, which will determine who controls Africa’s largest economy, top oil producer and an important U.S. counterterrorism ally. The poll comes at a crucial moment for democracy in Africa after a December poll in Congo was widely castigated as a fraud and opposition protests have been bloodily suppressed in Sudan.

The winner, in a bout between two heavyweights with a decades-long history in Nigeria’s patronage-based political system, will face sluggish economic growth, entrenched corruption and a dizzying array of security threats.

In one corner is President Muhammadu Buhari, the former military junta leader who returned to power in 2015 elections on a promise to defeat Nigeria’s Islamist insurgency and quell rampant corruption.

In the other, Atiku Abubakar, a former vice president and businessman whose dominance of the logistics sector brought him wealth and decades of graft allegations, is pledging to reinvigorate the country’s moribund economy.

Opponents Atiku Abubakar (left) President Muhammadu Buhari (right)

Polls show a race that is too close to call, with Mr. Buhari as the narrow favorite, armed with the advantages of incumbency and a broader base among the more populous Muslim north.

Officials from the U.S. and European Union have expressed concern that the closeness of the race will encourage vote rigging and the mobilization of thugs and security forces to intimidate voters.

Both candidates’ parties criticized the delay on Saturday, but called for calm.

Mr. Buhari’s governing All Progressives Congress called the news a “huge disappointment” but counseled voters to be patient. Mr. Abubakar’s opposition Peoples Democratic Party said the shoddy arrangements were a deliberate predetermined agenda by Mr. Buhari to cling on to power.

At least three Electoral Commission offices have been torched in recent weeks, against a backdrop of entrenched violence that includes Islamist insurgencies in the north, piracy in the south and religiously tinged battles over farmland in Nigeria’s central regions. On Wednesday, a state governor’s motorcade was attacked by Islamist militants, who killed at least five members of his security detail.

Regional governors have warned that poor security could frustrate efforts to hold elections across parts of the north. Nigeria’s army has pledged to deploy 95% of its troops during the election weekend. Mr. Buhari said in a televised address on Thursday that he is committed to free and fair elections. …

The country has been dealing with pockets of instability in the run-up to the vote. Authorities on Friday reported that 66 people had been killed in the state of Kaduna in communal violence just hours ahead of the polls. Reinforcements from the security forces were fanning out across Maiduguri, the capital of the northeastern Borno state, amid fears that Boko Haram or its offshoot Islamic State in West Africa Province, could launch attacks to coincide with the polls.

Published at WSJ .com on February 16. Reprinted here for educational purposes only. May not be reproduced on other websites without permission from The Wall Street Journal.