Police in northern Nigeria say gunmen have attacked two police stations in Kano, leaving two civilians dead.

Authorities say the civilians were killed late Sunday during a shootout between police and the gunmen. The attackers also threw bombs at the police station, damaging the building.

Gunmen launched a second attack early Monday on a station that was targeted last week, but there were no reports of any casualties.

No group immediately claimed responsibility for the attacks.

The radical Islamist group Boko Haram has said it was responsible for 185 deaths in recent weeks in Kano, Nigeria's second largest city.

Boko Haram says it is fighting to implement a strict interpretation of Sharia law across Nigeria.

The ongoing violence has raised concerns that Nigeria, Africa's most populous country and its biggest oil producer, is sliding toward civil war.