A bomb exploded outside a stadium in northern Nigeria on Monday, just minutes after President Goodluck Jonathan left a campaign rally at the site.
Police say at least one female suicide bomber was involved in the attack in the town of Gombe. Rescue workers say a second female bomber may have also died in blast. Eighteen people were treated for injuries at a local hospital.
There was no claim of responsibility for the blast in the town of Gombe, but suspicion is likely to fall on Boko Haram militants who have attacked the area several times. On Sunday, a suicide attack in the town killed five people.
Workers collected bodies from the streets of Maiduguri on Monday, a day after the Nigerian army repelled an attempt by Boko Haram militants to take control of the city.
One Nigerian security officer said at least 500 militant fighters were killed in Sunday's battles, although that number has not been confirmed.
A reporter for VOA in Maiduguri, Abdulkareem Haruna, said many civilians were killed, some from fighting alongside the soldiers, others by stray bullets and bombings by the Nigerian Air Force.
Hundreds of civilians armed with hunting rifles, clubs and machetes were seen advancing toward the fighting on Sunday, saying they wanted to help the soldiers stop the militants.
Borno state governor Kashim Shettima said Boko Haram attacked Maiduguri along two main roads, with the intention of killing "a massive population of residents and internally displaced persons" who had taken refuge in the city from other parts of the state.
He saluted both soldiers and civilian fighters, saying he is confident the Boko Haram insurgency can be overcome.
This was Boko Haram's second failed attempt to seize the Borno state capital. The attack came two weeks before Nigeria's February 14 general election.
Major General Chris Olukolade told VOA this second attack was a "desperate run" by Boko Haram as the militants are pressured by Nigerian forces and troops from neighboring countries.
"We will do everything to keep Maiduguri and the neighboring provinces very safe from these terrorists," he said. "The mission is on. There is no allowing terrorists anywhere. As many times as they come, it will only give us the opportunity to decimate them."
On Saturday, Chadian forces reclaimed the northeastern Nigerian town of Gamboru-Ngala, after a heated battle with Boko Haram that involved a ground and air campaign. Gamboru-Ngala, about 145 kilometers east of Maiduguri, was captured by Boko Haram last year.
A soldier involved in the operation said Chadian forces were working under the African Union agreement for member states to help Nigeria in its fight against Boko Haram.
The African Union has agreed to move forward with a proposal to send 7,500 troops to fight the Boko Haram insurgency.
The conflict, which began in 2009, has forced more than a million people from their homes and killed some 10,000 people in the past year alone, according to the Council on Foreign Relations.
The Nigerian army has struggled to contain Boko Haram, which has said it is taking territory for a caliphate ruled by Islamic law.
Last April, Boko Haram sparked international outrage when it kidnapped 276 schoolgirls from the remote Nigerian town of Chibok. Dozens have managed to escape, but more than 200 remain missing.