At least six civilians and six members of a youth vigilante group were killed in an attack by Boko Haram militants on Nigeria's northeastern city Maiduguri, two military sources said on Thursday.
The attack was reported late on Wednesday in Maiduguri, which is the capital of Borno state and the birthplace of the Islamist jihadi group.
One of the sources said the vigilantes in the so-called civilian joint taskforce died after they mistook female suicide bombers for residents fleeing the Boko Haram raid.
Boko Haram, which has killed thousands in its attempt to carve out an Islamist state in the country's northeast, is on the backfoot foot following a co-ordinated offensive by military forces from Nigeria, Niger, Chad and Cameroon.
However, Wednesday's assault shows it is still capable of pulling off bloody assaults.
Defence spokesman Major General Chris Olukolade said the insurgents began their attack on the outskirts of Maiduguri with the detonation of two female suicide in Ladi Kayamla area.
He said the attack was likely intended as a diversion to "slow down the ongoing assault on the Sambisa forest, it was carried out by those insurgents escaping from locations that have been destroyed".
Boko Haram has become scattered across Borno, but maintains a final stronghold in the Sambisa forest reserve. Nigeria began a ground assault on the area in April and said it has overrun many camps and freed over 700 abducted women and children.
The army imposed a 24 hour curfew on Maiduguri following the attack.