Attackers with guns and explosives have raided a jail in a restive Nigerian city, leaving four prison guards dead, though it was not yet clear if any inmates were freed, authorities said.
The raid occurred in the northeastern city of Damaturu, previously hit by heavy violence blamed on Islamist group Boko Haram and which last week saw gun battles between security forces and extremists that killed at least 40 people.
However, it was not yet known who the attackers were and whether any Boko Haram members were being held in the jail.
The raid saw attackers throw two explosives and open fire, forcing their way into the central prison in Damaturu, a prison officer said.
Boko Haram's insurgency has killed hundreds, mainly in Nigeria's north. The group has previously targeted prisons and freed Boko Haram members.
On Friday, President Goodluck Jonathan fired his national security adviser and defence minister amid growing fears over spiralling violence in the north of Africa's most populous nation and largest oil producer.
