At least 12 people were killed at police headquarters in Gombe, in the northeast. Police have not confirmed if all the victims were officers, but they do suspect members of the radical Islamist terrorist group Boko Haram are behind the attack. Authorities repelled a second attack at a prison.
Also Friday night, in the northwest city of Kano, police say gunmen on a motorcycle killed five worshippers at a mosque. No one has claimed responsibility, but officials believe Boko Haram is involved in the attack.
Boko Haram has waged violent attacks in its campaign to implement strict Islamic law across Nigeria, which is roughly divided between Muslims in the north and Christians in the south.
The radical group claimed responsibility for one of the deadliest attacks in Kano last month that killed 185 people. It also admitted to killing at least 44 people in a Christmas Day bombing at a Catholic church outside Abuja, Nigeria's capital.
Following the Christmas attack, President Goodluck Jonathan declared a state of emergency in areas hard hit by violence blamed on Boko Haram.
Mr. Jonathan said the measure impacted parts of Yobe and Borno states in the northeast, Plateau state in central Nigeria, and Niger state in the east.
He said the temporary closure of borders in those areas was necessary to address security challenges and restore normalcy to the country.
The opposition has criticized the Jonathan administration for failing to control Boko Haram.