Nigerian Islamists stormed a police station in the restive northeast on Thursday, sparking a shootout that left four officers and five insurgents dead, police said.
The overnight attack happened in the remote Babban Gida village of Yobe state, an area repeatedly targeted by Boko Haram, the Islamist group blamed for killing hundreds in northern and central Nigeria since 2009.
"They came to attack our station there early this morning at about 1:00 am (0000 GMT) and our men engaged them in a shootout," state police chief Alhaji Sanusi Rufai said.
"We killed five of them but they fled with the corpses. Unfortunately, we also lost four of our policemen," he added, labelling Boko Haram gunmen as the suspected culprits.
Police stations have frequently been among the group's targets.
Boko Haram has said it wants to establish an Islamic state in northern Nigeria, but the group's demands have repeatedly changed.
Crippling poverty and frustration with government corruption are key factors fuelling the insurgency, analysts say.
Last week, Nigeria's presidency said it would study whether an amnesty for the Islamists could help curb the unrest.
Boko Haram's purported leader, Abubakar Shekau, dismissed any potential amnesty deal in an audio statement obtained by AFP earlier Thursday.
Nigeria is Africa's most populous country and top oil producer, roughly split between a mainly Muslim north and mostly Christian south.