Maiduguri - Two attacks by suspected Boko Haram insurgents have killed 24 people in the latest violence believed to be in revenge against vigilantes, residents and officials said Tuesday.
A survivor and a hospital source spoke of 18 people killed in the town of Bama on Sunday. A resident and a military source said six people were killed in Damasak on Monday.
The two locations are in Borno state, but are some 200km apart.
The military has encouraged the formation of vigilante groups to help it track down Boko Haram members as it pursues an offensive in the northeast aiming to end the Islamist extremists' four-year insurgency.
"They came in military uniform and pretended to be members of the JTF," survivor Mallam Bakura Module said of the attack in Bama, referring to a security task force.
"They asked after members of the vigilante group ... but they opened fire on members of the group as we assembled for an address, killing 14 persons and injuring 10 others."
An official at the University of Maiduguri Teaching Hospital said on condition of anonymity that four others had died on Monday night, bringing the death toll to 18.
In Damasak along the border with the neighbouring nation of Niger, relatives said vigilantes were traced there after travelling to the community to sell goods at the local market.
"They were shot in the middle of the night while sleeping in the [guest] house," said one relative, Mallam Ali Abdullahi.
A military official speaking on condition of anonymity confirmed the attack.
Dressed as soldiers
The violence was the latest in a spate of such attacks apparently targeting vigilantes and local residents' cooperation with them.
Vigilantes have been credited with helping to push the insurgents out, but security analysts have warned that the situation risks spiralling out of control and resulting in further violence in the future.
Last week, insurgents dressed as soldiers opened fire on worshippers leaving a mosque in the far northeastern village of Dumba, killing at least 35 people.
Separately earlier this month on 10 and 11 August, suspected Boko Haram members stormed a mosque in Konduga and shot dead 44 worshippers as well as 12 other people in a nearby village in another area of the northeast.
Nigerian President Goodluck Jonathan declared a state of emergency in the northeast in May and the military immediately launched a major offensive in the region aiming to end Boko Haram's insurgency.
The pattern of attacks that has occurred since then indicates the insurgents may have to a large degree scattered into more remote areas of the region.
There appeared to be an initial decline in the number of attacks in the region after the launch of the offensive, but violence has nonetheless continued, including particularly brutal attacks on three schools that left dozens of students dead.
Boko Haram's insurgency has left more than 3 600 dead since 2009, including killings by the security forces, who have been accused of major abuses.