An armed gang killed at least 40 members of village self-defence groups in a weekend ambush and related attack in Nigeria's central Plateau state, the Red Cross and residents said on Tuesday.
One resident described the assaults as a "revenge" attack on local vigilante groups set up to defend communities from the gangs.
For years, the heavily armed gangs — locally known as "bandits" — have intensified assaults in rural areas in northwest and central Nigeria where there is little state presence, killing thousands and conducting kidnappings for ransom.
Plateau state Red Cross secretary Nuruddeen Hussain Magaji said "hundreds of vigilantes were ambushed" on Sunday, and 30 were killed in the village of Kukawa.
That attack came as the vigilantes regrouped after clashes earlier in the day in the nearby community of Bunyun Nyalum left 10 vigilantes dead, said Musa Ibrahim, a resident.
Usman Nyalum, another resident, said the assault on Bunyun Nyalum came after a recent mobilisation of vigilantes in the area killed scores of bandits.
"Since the killing of the bandits by our vigilantes, the remaining bandits keep on trying... to take revenge," he said.
Magaji, the Red Cross official, warned the toll could rise as "more dead bodies of the vigilantes will be recovered from the bush".
Officials and residents confirmed the attacks overnight, though without concrete death tolls.
Weak policing
Nigeria's restive Plateau state also regularly sees deadly clashes between herders and farmers over land and natural resources.
Much of the violence in Plateau occurs in areas with little state presence, giving criminals a sense of impunity, researchers say.
The creation of government-backed militias and self-defence vigilante groups has expanded the Nigerian security apparatus both formally and informally, with mixed results.
In June, government-backed vigilantes killed more than 100 bandits in a gun battle in the northwestern state of Zamfara.
With government backing, they stormed the stronghold of Bello Turji, a notorious "bandit" kingpin, though he escaped.
Despite the efforts of the military, police and self-defence groups, violence continues across rural Nigeria, both from bandits as well as militants, whose stronghold is in the northeast.
Local groups can often find themselves overwhelmed or provoke harsh retaliation from the bandits for fighting back.
Although bandits have no ideological leanings and are motivated by financial gains, their increasing alliance with militants is a concern for authorities and security analysts.
