IBADAN, Nigeria - A bomb exploded Friday at an election office in Nigeria on the eve of the first of the oil-rich nation's three crucial April elections, authorities said, killing some officials in violence reminiscent of the country's flawed 2007 vote.

The explosion also gravely wounded others working at the Independent National Electoral Commission office in Suleja, a city in Niger state near the country's capital of Abuja, said Yushau Shuaib, a spokesman for Nigeria's National Emergency Management Agency. Electoral commission spokesman Kayode Idowu confirmed there had been deaths, but said he had no figures for the killed and wounded.

Suleja already saw a bombing at a political rally in March, an explosion that killed at least four people and left another 20 wounded. Shuaib said authorities still were trying to determine what kind of explosive was used in the attack Friday afternoon.

Nigeria's delayed first national election starts Saturday, with the bombing just one of a series of worrying signs recently seen across Africa's most populous nation. Coupled with a failed bombing in the north and an attack by a radical Islamic sect Friday, these signs undoubtedly prove worrying for international observers concerned about one of the top crude oil suppliers to the U.S., as well as those who will place their inked fingers to the ballots.

"Millions of voters may be disenfranchised by being too scared to go out to cast their votes," recently wrote Kunle Amuwo, an analyst with the International Crisis Group. "Politicians who orchestrate violence must be held accountable and prosecuted. Unless violence is swiftly curtailed and contained, there will be no basis for credible elections."

Nigeria, home to 150 million people, will vote Saturday on who should represent its citizens in its National Assembly. The positions remain highly lucrative, with more than $1 million in salaries and benefits, plus the ability to direct a swollen budget in a nation where billions in oil revenues routinely go missing.

The election was to be held last Saturday, but national election chairman Attahiru Jega stopped it after ballot papers and tally sheets went missing in many of the country's roughly 120,000 polling stations. Jega twice postponed the election and about 15 per cent of the races won't be held Saturday as misprinted ballots delayed them.

Nigeria's crucial presidential election, as well as local elections, will take place later this month.

Many hoped Jega, a respected academic, would be able to lead Nigeria out of its dark history of flawed polls marred by violence and ballot-box stuffing since it became a democracy in 1999. However, even he appears now to be overwhelmed by the logistical challenge of conducting elections in a nation twice the size of California that lacks reliable roads and railways.

"One man alone cannot overcome significant systemic and logistical challenges, nor can one person or one electoral event transform a political culture in which stolen elections and disregard for basic democratic principles have been the norm for decades," Johnnie Carson, the top U.S. diplomat for Africa, said in a speech Tuesday.

Outside of Jega's influence, politicians maintain murky ties with local gangs and militants from the nation's oil-rich southern delta to its arid north. Human Rights Watch estimates at least 85 people have died in recent months in political violence.

In some areas, election problems appear to have already begun.

In Borno state, police say gunmen from a radical Islamic sect known locally as Boko Haram shot and killed four people at a police station in Shani, including a local official of the country's ruling People's Democratic Party. The attack comes after suspected sect members wounded two officers guarding a church Thursday in Maiduguri. The sect already has killed a leading gubernatorial candidate in the state and appears to attack at will despite a security crackdown.

In Katsina state, a police spokesman says a local politician hired thugs to beat an election official and steal 200 ballots after Saturday's failed vote. Those unmarked ballots could, in theory, be used to cast votes in this weekend's rescheduled poll.

In Kaduna state, officials say a man carrying a bomb died when the explosive detonated Friday, wounding another man. Authorities found two other explosives in the dead man's home, though they immediately didn't have a motive for the bomb manufacturing.

Security remains a top concern in the country. An attacker tried to ram a tanker truck loaded with fuel and gas cylinders into the electoral commission's headquarters in Abuja before a 2007 election. The truck ran into barriers and stopped before reaching the building.

As a security precaution, officials closed Nigeria's land borders Friday. In Ibadan, a city in southwest Nigeria where fighting remains common, police roared down streets in armoured tanks with screaming sirens. One military vehicle appeared to ferry election materials to distribution centres.

During Nigeria's failed 2007 election, Ibadan and surrounding Oyo state saw everything from fake police officers stuffing ballot boxes to political operatives pushing the fingers of the confused elderly to vote for their party, according to a European Union report on the polls. Violence followed.

Oyo state police spokesman Olatunji Ajimuda told The Associated Press on Friday that such violence wasn't likely, as security agencies would patrol the streets and enforce a nationwide curfew. However, he acknowledged the power the nation's wealthy elite and politicians wield.

"Politics is a game," Ajimuda said. "We just hope the politicians play it that way."