Nigerians hit by failures in new election technology return to the polls on Sunday, to allow them to cast their ballots in the country's close-run presidential election.

President Goodluck Jonathan -- who is running against former military ruler Muhammadu Buhari -- and at least three governors from his ruling party were among those whose biometric details could not be checked by the devices, which are designed to combat electoral fraud.

Instead, they had to be processed by hand. Jonathan's Peoples Democratic Party (PDP) called it a "huge national embarrassment" and a "vindication" of their position against the technology.

"There should have been a test-run for a smaller election before deploying it for an election of this magnitude," said Jonathan's presidential campaign spokesman Femi Fani-Kayode.

Buhari, Jonathan's main opponent whose All Progressives Congress (APC) party had backed the voter identity card readers, however, suggested the row was overblown.

"All this, I think, negative thought about Nigeria election shouldn't hold because of (a) problem in even a maximum of five states," he said.

A 24-hour extension to the election was "in order", he added after voting in his home state of Katsina, in the Muslim-majority north.


Boko Haram


The confusion over the malfunctioning technology added to problems in voting in Africa's most populous nation which included election officials arriving late -- or sometimes not at all.

Boko Haram, which has dominated the campaign trail, also loomed large, apparently holding good to their pledge to disrupt what it sees as the "un-Islamic" elections by launching a series of attacks.

On Friday, 23 people were beheaded and homes set on fire in Buratai, some 200 kilometres (125 kilometres) from the Borno state capital, although it was not clear if it was poll-related.

On Saturday, at least seven people were killed in a string of shootings that witnesses blamed on the Islamists in the northeastern state of Gombe. Three of the attacks were at polling stations.

An election official in the Nafada district, who asked not to be identified, said the gunmen were heard shouting: "Didn't we warn you about staying away from the election?"

The Islamists have repeatedly targeted Nafada but the APC on Saturday blamed its political opponents.


Enforced delay


Sunday will again see tight security in place for the vote from 0700 GMT, given Nigeria's past history of poll-related violence that in 2011 saw some 1,000 people killed after the result was announced.

The Independent National Electoral Commission (INEC) had said the overall result would be announced within 48 hours of polls closing.

But the enforced delay, which will see those affected by the technical glitches accredited by hand, will likely stretch an already loose deadline.

INEC chairman Attahiru Jega told NTA state television in an interview on Saturday night that what happened to Jonathan was "regrettable and a national embarrassment".

But he added that "in general, we believe that in spite of the challenges things have gone very well" and that turn-out was "quite large".

The body's spokesman Kayode Idowu said voting would take place on Sunday in "just about 300 polling units out of about 150,000" across the country.

"These include about 109 places where cards were not read. Barely 100 places with biometrics issue and others had issue with batteries," he told reporters in the capital, Abuja.

"There are some states without any such incident at all."


Close-run


The problems come with close interest in Nigeria's presidential election, which is the mostly keenly fought in the country's history.

Retired army general Buhari, who headed a military government in the 1980s, has repeatedly attacked Jonathan's record on tackling Boko Haram, rampant government corruption and the economy.

Jonathan have portrayed the 72-year-old Buhari as yesterday's man, warning that his reputation as a bulwark against graft and "indiscipline" is a cover for dictatorship.

Both men have been seen as neck-in-neck in rare pre-election polling with the real possibility that the PDP could be defeated for the first time since the return to civilian rule in 1999.

Observers have, however, seen the six-week delay in voting from February 14 on security grounds as a ploy for Jonathan to claw back lost ground using the greater power of incumbency.

Voting is also taking place for the country's parliament.