BAUCHI: Nigeria's president called for calm on Sunday after at least 86 people died in clashes between farmers and semi-nomadic herders over the weekend.

Authorities imposed a dusk-to-dawn curfew in central Plateau state after the fighting, part of an escalation of clashes that have raged for years, often over dwindling fertile land.

A total of 86 people had died by late Sunday, state police spokesman Terna Tyopev said, raising the local government's earlier estimate of 70.

The violence in Nigeria's diverse Middle Belt states has now killed more people than the Islamist insurgency in Nigeria's northeast, according to Reuters calculations.

Insecurity has become a major electoral problem for President Muhammadu Buhari, who plans to seek re-election in February and who won power on pledges to deliver peace and stability.

In a statement on the president's official Twitter account late on Sunday, Buhari appealed for calm, adding that "no efforts will be spared to bring the perpetrators to justice, and prevent a recurrence."

But senior lawmakers lamented the state of Nigeria's law enforcement systems.

"This further strengthens my constant call for an overhaul of the entire security apparatus of this country," Yakubu Dogara, the leader of Nigeria's lower house of parliament, said in a statement on Sunday.

Buhari's party rejects criticism that his administration is soft-peddling justice for the herders, who belong to the same Fulani ethnic group as the president.