Spokesman Sagir Musa said in a statement that a lieutenant also was killed in the shootout that began when troops were ambushed at a road barricade in Abonnema. The confrontation was one of several reported killings on Saturday. Police in Rivers state said a former aide to the governor was shot dead along with his brother.
The Nation newspaper reports that three people were killed in Lagos when thugs attacked a polling booth and burned ballot boxes.
Some Nigerians who were shaken by an extremist attack in the country's troubled northeast say they stayed away from the polls on Saturday.
Maiduguri resident Haruna Isa says he feared for his life after hearing multiple blasts. Nigerian security forces at first denied an attack and called the blasts a show of force to deter extremists. They later acknowledged that Boko Haram extremists "attempted to infiltrate" the Borno state capital by launching artillery fire.
Isa says that "I don't trust anyone anymore," including politicians who might vow to bring security to the troubled northeast.
Asmau Hassan, one of the tens of thousands of people displaced by extremist violence, says she lost her voting card in the morning confusion after an explosion at her camp. She says she feels hurt because she wanted to vote for President Muhammadu Buhari but "I have just turned into an onlooker now."
As vote-counting proceeds in Nigeria's election, opposition candidate Atiku Abubakar lost at his home polling station in the northern city of Yola. When votes were added up at the polling station where Abubakar cast his ballot earlier Saturday, President Muhammadu Buhari came in first with 186 votes to Abubakar's 167. A large crowd broke into jubilant cheering when officials announced Buhari's victory in that polling place. "Next level," some chanted, citing Buhari's campaign slogan.
Election observers expect that national results will be announced within two to four days.
In Nigeria's largest city, Lagos, counting started in many areas, although voting continued in some polling units where the exercise started late because of the delayed arrival of electoral officials and materials.
During the voting there were some isolated cases of violence. In the Okota neighborhood of Lagos, thugs disrupted the exercise, setting ballot boxes ablaze.
A few cases were reported of hooligans trying to force people to vote for particular candidates, but in most areas voting took place in an orderly way.
As vote counting begins across Nigeria, some party agents recite aloud in unison as polling officials hold ballot papers aloft one by one.
"I'm feeling fine now!" declared Nura Abba, an agent for the ruling party as several polling stations swung into counting in a schoolyard in the northern city of Kano.
One electoral commission presiding officer at another polling station in the dusty schoolyard, Kabiru al-Haji Musa, held up that station's presidential results, scrawled in blue ballpoint pen.
President Muhammadu Buhari received 88 votes. Top challenger Atiku Abubakar, eight.
Turnout was down in this election, Musa said, and he wasn't sure why. They expected more than 390 voters at the station but saw only 102, he said.
"Everything was normal. No violence, no interruption, no cheating," the 30-year-old said, standing barefoot after a day that began around dawn.
He said security is Nigeria's most pressing issue but didn't vote himself, saying that as he was working at the polls he wasn't allowed.
Nigerian security authorities are now openly acknowledging an extremist attack in the northeast city of Maiduguri shortly before voting began on Saturday.
A statement by Borno state police says Boko Haram extremists "attempted to infiltrate" the state capital by launching artillery fire, likely to disrupt the elections.
The statement says "some missiles strayed into vulnerable locations" but there were no casualties and the extremists retreated.
Security sources, however, say one soldier was killed and four wounded.
Nigerian security forces earlier Saturday said the reported blasts had been their own in a show of force to deter extremists.
— Ibrahim Alfa Abdulrahim
Vote-counting has begun in Nigeria even as many people who were in line by the 2 p.m. closing time will continue to cast their ballots in the hours to come.
More than 72 million Nigerians were eligible to vote in this election as President Muhammadu Buhari seeks a second term in Africa's most populous nation and largest economy.
Both Buhari and top challenger Atiku Abubakar declared they will win the election that many observers see as too close to call.
The vote has been marked by violence in the northeast and south, and in some parts of the country polling stations didn't open for several hours.
After a surprise last-minute election delay a week ago, officials believed another postponement would be disastrous, even if it meant a bumpy day of voting.
A Nigerian military official says a military outpost in the northern state of Yobe was attacked early Saturday, before voting started.
Military spokesman Col. Musa Sagir confirmed the attack on Geidam, hometown of Yobe's governor, saying it happened at 6:30 a.m.
The statement said the attack was repulsed and there were no casualties, adding that the situation is now calm in Geidam, allowing people to vote.
Boko Haram, the Islamic extremist group, is active in northern Nigeria.
There were also blasts in Maiduguri, the capital of Borno state, shortly before polls opened that police said they triggered for "security calculations" in a show of force to deter Islamic extremists.
A coalition of civic groups says multiple polling units across Nigeria have not opened more than four hours after the official start of the voting.
In Twitter posts, the Nigeria Civil Society Situation Room said many polling stations are late in opening because of several problems including missing stamps, the late arrival of polling officials and faulty card readers. States affected by late openings of polling stations include Akwa Ibom and Lagos, Nigeria's largest city.
Nigeria's electoral commission postponed the presidential election, initially set for Feb. 16, by a week, saying it needed more time to organize the logistics for a credible election.
The election is widely seen as a tight race between President Muhammadu Buhari and his main rival, former vice president Atiku Abubakar.
Nigeria's top opposition challenger Atiku Abubakar has cast his ballot in a presidential election that observers say is too close to call.
He tells reporters that "I look forward to a successful transition" and says he is impressed with voter turnout. The billionaire former vice president and frequent contender voted in his hometown of Yola in the northeast.
He previously pledged to accept the results of the election, provided they are credible.
President Muhammadu Buhari was among the country's first voters and told reporters he is ready to congratulate himself.
Some Nigerians are reporting low turnout or the late opening of polls more than one hour into the presidential election.
Only a few people are in line at one polling station in Maiduguri in the northeast as local media urge voters to the polls after gunfire was heard earlier in the morning. Police have tried to calm panicked residents, calling the blasts a show of force to deter Islamic extremists.
The spokesman for President Muhammadu Buhari's campaign, Festus Keyamo, says on Twitter that no electoral commission workers are in sight at his polling station in Delta state in the south. He says the commission's local office is a short walk away and asks: "What's going on?"
A large number of foreign and local observer groups are tracking polling stations.
Nigeria's president says he will be congratulating himself at the end of the election after he was among the first Nigerians to cast their ballots.
A jovial President Muhammadu Buhari brushed aside reporters' questions about whether he would accept a loss to top challenger Atiku Abubakar in a race some observers now see as too close to call.
Buhari, voting in his northern hometown of Daura, jokingly checked the ballot his wife was casting to see whom she had voted for.
The president called the voting process smooth but in other parts of the country some officials were reporting concerns with a delayed opening of polls and a heavy security presence perhaps intimidating potential voters.
Nigerians have begun voting in a presidential election one week after a surprise last-minute delay blamed on logistical challenges.
President Muhammadu Buhari has cast his ballot as he seeks a second term in a race that observers now say is too close to call with top challenger and former Vice President Atiku Abubakar.
The ailing Buhari has been criticized for not delivering enough on his promises to tackle insecurity, the economy and corruption. Abubakar points to his business success in making sweeping pledges to turn the economy around but is dogged by corruption allegations.
Gunfire has been heard in at least two cities shortly before the polls opened, but police in Maiduguri in the northeast called the blasts there a show of force by security forces.
Multiple blasts in Nigeria's northeast are opening election day as President Muhammadu Buhari seeks a second term in Africa's most populous nation.
The blasts in the Borno state capital of Maiduguri came shortly before polls were to open. Police there say it was for "security purposes" and not an attack.
Gunfire also has been heard in parts of Port Harcourt in the restive south, where the military presence is said to be heavier than in past elections.
Buhari in a final address to the nation on Friday vowed that the more than 72 million Nigerians who can vote in this election would be able to go to the polls in peace.
But the Boko Haram extremist group, its Islamic State-affiliated offshoot and various agitators across the country have other plans.