The death toll from Tuesday's fighting between the Fulani and Tarok Nigerians has been slow to emerge, parlty because of non-functioning telephone lines, Red Cross officials said.
But the fighting has been occurring in six remote farming villages on the border between Plateau and Taraba states.
"It must have been more than 100, but we cannot confirm a specific number of dead," a Nigerian Red Cross Society official said, adding that 5500 people were displaced.
Local media have reported fighting in the villages of Old Sarkin Kudu, New Sarkin Kudu, Auoshima One, Auoshima Two, Angon Masu and Sabon Layi.
The latest attacks brings the death toll from two-and-a-half months of tit-for-tat violence to at least 350, according to unofficial figures.
Land and cattle
The Fulani, who live principally from cattle herding, and the Tarok, who are subsistence farmers, are fighting mainly over land and cattle.
Most of the killing is done with large cutlasses and in arson attacks.
Abu Baqr Sadiq Muhammad, head of political science at Nigeria's Ahmadu Bello University, said the dispute was rooted in competing claims over land between nomadic cattle herders and settled farmers.
But it had been compounded by irresponsible allocation of land by government and rising crime levels.
"You cannot reduce the problem to religious differences," he said.
Local police were not immediately available for comment. Nigerian authorities routinely do not provide death tolls from such fighting, for fear of provoking reprisal attacks by groups allied to the victims.
A similar outbreak of fighting in Plateau state in 2001 killed at least 1000 people.