A group of around 150 assailants have shot and hacked to death at least 19 people and seriously injured six people in a village in northwest Nigeria, police said.
The attack took place on Saturday in Lingyado, in the state of Zamfara, which sits at the base of the Sahel where Africa's most populous nation borders Niger.
"We have confirmed the death of 19 people in an attack on Lingyado village by gunmen believed to be armed robbers out to avenge the extra-judicial killing of their comrades by local vigilante groups," said Tambari Yabo, state police commissioner.
The vigilantes had previously attacked suspected armed robbers who have been targeting the area, he said.
"It is the suspected robbers that escaped the vigilante operation that have been behind this attack and similar ones in retaliation," the commissioner said.
He said a number of houses and vehicles were burnt in the attack and joint military-police teams had been deployed to the area. No arrests had been made.
A senior police officer said on condition of anonymity that "the gang of armed robbers moved door-to-door, shooting or hacking their victims to death" and included around 150 assailants. He said the victims included children.
On August 10, a number of victims were killed in similar circumstances by suspected armed robbers in attacks on two villages in the area.
Islamist sect Boko Haram has been blamed for scores of attacks in Nigeria's north, but there was so far no indication of the group's involvement in Saturday's raid.