Gunmen in Nigeria have killed dozens of people and kidnapped a number of children in separate attacks in two northern states, police and residents said on Sunday, the latest incidents in a region dogged by armed violence.

Armed gangs on motorbikes frequently take advantage of thinly stretched security forces in the region to kidnap villagers, motorists and students for ransom.

Residents said armed men had attacked Janbako and Sakkida villages in northwestern Zamfara state on Saturday, killing 24 people. The gunmen also abducted several children who were collecting firewood in a forest in neighbouring Gora village.

Hussaini Ahmadu and Abubakar Maradun, local residents in Janbako and Sakkida, told Reuters by phone that the gangs had earlier in the week demanded villagers pay a fee to enable them to farm their fields, but villagers did not do so.

Zamfara police spokesman Yazid Abubakar confirmed the attacks but said only 13 people had been reported killed and nine young boys and girls kidnapped.

In north central Benue state, gunmen killed 25 people and set their houses on fire during an attack on Saturday on the Imande Mbakange community, two residents said. The motive of the attack was not known.

Police did not immediately respond to requests for comment.