Fifty-three people have been killed and 13 villages burnt in central Nigeria's Benue state, local MP Sule Audu has told the BBC.
The conflict, which started last week, is said to have been caused by a long-running dispute over land ownership between cattle herders and farmers.
Forty people were killed on Sunday, in the worst attack carried out by Fulani herdsmen since last week, Mr Audu said.
Nigeria is affected by a spate of conflicts over land, religion and oil.
The violence in Benue is the latest sign of the growing security challenges facing the government, reports BBC Nigeria correspondent Will Ross.
Last week, President Goodluck Jonathan cut short a trip to South Africa to deal with a spate of deadly attacks.
'Security forces deployed'
People from the Fulani community confirm they carried out a series of raids on the rival Agatu farming community after several hundred of their cattle were stolen, our correspondent says.
However, they deny killing as many 53 people, he adds.
Mr Audu, who represents the Agatu community, told BBC Hausa it was unclear what caused the violence.
"Fulani herdsmen have hired some mercenaries to attack us and we don't know the reasons for these attacks," he said.
A police spokesman said security force members have been deployed to the area to restore stability.
He could not confirm casualty figures.
Last week, more than 40 policemen were killed in Nasarawa state in an attack carried out by the outlawed Ombatse cult.
Islamist group Boko Haram continues to stage attacks in the mainly Muslim north - it has killed some 2,000 people in the past three years.