Bomb blasts struck three different locations in Nigeria on Tuesday, amid tensions caused by the coming elections and Boko Haram insurgency.
In the first reported attack, a VOA Hausa service reporter says multiple blasts hit a military checkpoint in Biu, in northeastern Borno state, killing 12 people. According to local media, two suicide bombers riding a three-wheeled vehicle were stopped at an entry checkpoint, where they dismounted their vehicle and detonated their explosives.
Other reports say soldiers killed 17 militants who fired on them after the blasts.
A second attack took place in the city of Potiskum, in nearby Yobe state. Police say a suicide bomber blew himself up at a restaurant, killing three people and wounding 12.
Boko Haram has launched previous attacks in both locations.
Meanwhile several explosions occurred and gunfire erupted at a political rally for the opposition APC party in Okrika, a town in southern Rivers state. The APC is challenging the ruling PDP party in presidential and parliamentary elections next month.
There were no immediate claims of responsibility for any of the attacks.
Earlier Tuesday, witnesses reported that Boko Haram fighters stormed the Borno state city of Askira Uba and burned much of it down.
Fleeing residents say militants first raided Askira Uba in Borno state on Sunday, torching the home of the city's top official. They say the militants returned late Monday and set fire to homes and public buildings.
Also Monday, suspected Boko Haram militants killed five soldiers during a cross-border attack in northern Cameroon.
Cameroon's military said Tuesday the soldiers were killed during a "series of clashes" with the militants the day before. Officers say Boko Haram attacked a military base in the Waza region, but were driven back. The army says many of the attackers were killed.
Cameroon, Niger and Chad are helping Nigeria fight the Islamic extremist group. In response, Boko Haram has launched attacks in all three countries during the past two weeks.
On Monday, representatives of the Economic Community of Central African States met in Cameroon's capital, Yaounde, and announced they are contributing $86 million to help fight the militants.
On Tuesday, the commander of U.S. Special Forces Operations in Africa, James Linder, told the Reuters news agency that the United States will provide communications equipment and intelligence to the effort.
Boko Haram has killed thousands of Nigerians during the past five years and controls numerous towns and villages in the northeast. Regional concern grew after the extremists seized a multinational military base last month on Lake Chad.
Boko Haram has warned Nigerians not to take part in the March 28 elections. The polls were originally scheduled for February 14 but electoral officials postponed them, saying Boko Haram posed too big a security threat.
Analysts say the APC poses a strong threat to the PDP. President Jonathan has come under intense criticism for failing to stop the insurgents or rescue more than 200 girls kidnapped by Boko Haram from the village of Chibok in April 2014.