Nigeria's presidency late on Sunday announced "deeply unfortunate killings across a number of communities" in central Plateau State.
Earlier one police report said 86 people were killed in clashes between mostly Muslim herders and Christian farmers.
President Muhammadu Buhari appealed for calm as the military and police tried to end the bloodshed, and said "no efforts will be spared" to find the attackers and prevent reprisal attacks.
Nigeria's government did not announce a death toll. But the independent Channels Television cited a Plateau State police spokesman, Mathias Tyopev, as saying 86 people had been killed, with at least 50 houses destroyed, in violence that appeared to have started overnight.
Deadly clashes between herders and farmers in central Nigeria are a growing security concern in Africa's most populous country, which is roughly split between Muslims in the north and Christians in the south.
The fighting between herders and farmers by some accounts has been deadlier than Nigeria's Boko Haram extremist insurgency, which continues to carry out attacks in the northeast.
That extremist threat has been cited as one cause of the growing tensions in central Nigeria as herders - also feeling the effects of climate change - are forced south into more populated farming communities in search of safe grazing.
Also on Sunday, Plateau State governor, Simon Bako Lalong, announced a 6 p.m. to 6 a.m. curfew. He said the incident was "unfortunate".