DAURA/YOLA, Nigeria (Reuters) - Nigerian authorities postponed Saturday’s national election by a week, just hours before polls had been due to open, prompting the opposition candidate to accuse President Muhammadu Buhari of seeking to “disenfranchise” voters.

The electoral commission said the postponement was due solely to logistical factors and denied political pressure had played any part in the decision. Buhari and his rival, former vice president Atiku Abubakar, both urged voters to stay calm.

Mahmood Yakubu, chairman of the Independent Electoral Commission, said the election would now be held on Feb. 23, adding that the date was “sacrosanct” and that campaigning would be suspended until then.

Buhari, in power since 2015, faces a tight election contest against Atiku of the People’s Democratic Party (PDP). Nigeria is Africa’s largest economy and its top oil producer.

Nigerians expressed dismay and anger over the delay, in a country where 84 million people have registered to vote. Past elections have been marred by violence, intimidation and ballot-rigging, and the postponement raised the possibility of unrest.

“They (the government) are not following the rule of law... This is a total ploy, it is not true that they are not ready” said opposition supporter Oscar Humphrey, 37, in the northern city of Kano, a key battlefield in the presidential race.

In President Buhari’s hometown of Daura in northern Nigeria, student Dauru Balarabi also expressed dismay, saying he had gone there specially to vote. “I spent my morning, my time, my energy for the elections so actually I am not happy,” he said.

The electoral commission’s Yakubu attributed the decision to delays in transporting electoral materials.

“(The postponement) has nothing to do with security, nothing to do with political influence, nothing to do with availability of resources,” he told a gathering of foreign election observers and reporters.

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He said some sensitive election materials had been distributed but all had been retrieved and returned to the central bank and an audit would now be conducted. In Nigeria the central bank stores election materials for safe keeping.

“DANGEROUS”

PDP chairman Uche Secondus said the postponement was “dangerous to our democracy”. He called it part of an attempt by Buhari to “cling on to power even when it’s obvious to him that Nigerians want him out”.

Buhari, who was Nigeria’s military ruler in the early 1980s, expressed disappointment over the delay but urged Nigerians in a statement to “refrain from all civil disorder and remain peaceful, patriotic and united”.

Atiku urged voters to be patient but later said Buhari’s administration was behind the delayed elections, without offering any evidence.

“By instigating this postponement, the Buhari administration hopes to disenfranchise the Nigerian electorate in order to ensure that turnout is low on the rescheduled date,” he said on Twitter.

Buhari’s spokesman Garba Shehu declined to comment.

Observer missions from the European Union, the African Union and other organizations urged Nigerians in a statement “to remain calm and supportive of the election process” and said the electoral commission must adhere strictly to the new date.

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“No matter who wins, it is now far more likely that the loser will contest the result and argue that the election has been compromised because sensitive materials are out there,” said Bismarck Rewane, economist and CEO of Lagos-based consultancy Finance Derivatives.

Situation Room, an organization of more than 70 civil society groups, said the postponement had harmed the credibility of the electoral commission, creating “needless tension and confusion”.

Nigeria’s presidential elections in 2011 and 2015 were also delayed over logistics and security issues.

Six people were killed in a bomb blast in the northeastern city of Maiduguri by suspected Islamist militants on Saturday morning, the State Emergency Management Agency said, despite increased security measures in much of the country.

Maiduguri is the capital of Borno, the state worst hit by the Boko Haram militant group and its offshoot, Islamic State in West Africa Province. Boko Haram had warned people not to vote.