Nigeria is facing serious security threats, from a grinding Islamist insurgency in the northeast, bandit militias in the northwest and separatist tensions in the southeast.

At least 74 people were killed in Nigeria's Benue state in two separate attacks by gunmen this week, local officials and police said on Saturday, the latest clashes in an area where violence between pastoralists and farmers is common.

Violence has increased in recent years as population growth leads to an expansion of the area dedicated to farming, leaving less land available for open grazing by nomads' cattle herds.

Benue state police spokesperson Catherine Anene said 28 bodies were recovered at a camp for internally displaced people in Mgban local government area between Friday evening and Saturday morning.

It was not immediately clear what triggered the attack but witnesses said gunmen arrived and started shooting, killing several people.

This followed a separate incident in the same state on Wednesday in the remote Umogidi village of Otukpo local government area, when suspected herdsmen killed villagers at a funeral, Bako Eje, the chairman for Otukpo, told Reuters.

Paul Hemba, a security adviser to the Benue state governor, said 46 bodies were recovered after Wednesday's attack.

President Muhammadu Buhari in a statement on Saturday condemned "the recent bout of killings in Benue State in which tens of people were killed in Umogidi community" and directed security forces to increase surveillance in affected areas.

Many such attacks in remote parts of Nigeria go unreported as thinly stretched security forces often respond late to distress calls by communities.

Benue is one of Nigeria's Middle Belt states, where the majority Muslim North meets the predominantly Christian South.

Competition over land use is particularly intractable in the Middle Belt, where fault lines between farmers and herders often overlap with ethnic and religious divisions.

In further violence, gunmen abducted at least 80 people in Zamfara state, a hot spot for kidnappings for ransom by armed gangs targeting remote villages, residents said on Saturday.