A military intelligence officer says soldiers have killed 20 Islamic extremists while two police officers died in an hours-long shootout near Maiduguri city in northeast Nigeria.

An army officer, meanwhile, says that in another attack Thursday, militants killed one soldier and abducted three others in Potiskum.

The officers requested anonymity because they are not authorized to speak to reporters on the record. Bala Ahmed, a taxi driver in the area, also said he witnessed the fight near Maiduguri.

Potiskum and Maiduguri are strongholds of Boko Haram, an Islamic extremist group behind numerous attacks in Nigeria.

Three northeast states covering a sixth of this West African oil producer have been under a state of emergency since May 14 as the military has tried to crack down on the extremists.