Witnesses say two separate explosions rocked the central Nigerian city of Kaduna on Tuesday, including one near a military base.
Police say one blast occurred near a bridge and the other took place at the base of the army's 1st Mechanized Division just outside Kaduna. Officials said there were an unknown number of casualties.
Police were investigating reports that the army base blast was caused by a suicide bomber who rammed a car through the front gates. Witnesses say soldiers cordoned off the area and blocked rescue workers from entering the site.
There was no immediate claim of responsibility for the blasts. The radical Islamic sect known as Boko Haram has been blamed for a surge in violent attacks against police, military and government facilities.
Kaduna is 200 kilometers south of Kano, where Boko Haram claimed responsibility for a wave of attacks that killed about 180 people last month.
The militant group has said it is fighting to impose strict Islamic law across Nigeria, but analysts say some attacks appear to be the result of political disputes.
Frequent bomb blasts and shootings in the north blamed on Boko Haram have prompted Nigeria's government to increase security.
President Goodluck Jonathan has declared a state of emergency in some parts of the region and vowed to defeat the group.