Suspected Islamist extremists have shot dead 44 worshippers in an attack on a mosque in Nigeria's restive northeast, a senior government official said on Monday.
"Gunmen believed to be Boko Haram members entered the mosque and opened fire on Muslim worshippers, killing 44," the official said on condition of anonymity because he was not authorised to speak publicly of the attack in Konduga on Sunday.
The official said the attack was believed to be in revenge over citizen vigilante groups forming to help the military battle Islamist extremist group Boko Haram, which has been waging an insurgency since 2009.
Some residents spoke of the attackers arriving wearing army camouflage, a tactic they have used in the past to disguise themselves, though those details had not been officially confirmed.
The attack came as Nigeria's military pursues an offensive in the country's northeast aimed at ending the insurgency, with a state of emergency declared in the region in May.
In recent weeks, the military has encouraged the formation of vigilante groups to help authorities locate and arrest members of Boko Haram.
The vigilante groups have been credited with reducing the number of attacks, but some have warned that the situation could spiral out of control and lead to further violence.
Boko Haram's insurgency has left at least 3,600 people dead since 2009, including killings by the security forces, who have been accused of major abuses.