Clashes between rival ethnic groups in eastern Nigeria's Ebonyi state on Saturday killed at least 50 people, the state government spokesman said, and police said mobile units had been sent to the state to quell the violence.

The clashes erupted from a long running rivalry between the Ezza and Ezilo people of Ishielu district that periodically flares up.

There was no suggestion it had anything to do with wider security problems in the country stemming from a violent Islamist insurgency that set off a wave of deadly bombs on Christmas Day.

But they are likely to add to President Goodluck Jonathan's mounting security woes at a time when his forces are stretched.

"Up to 60 people died in the violence. It is difficult to give the exact figure because when we visited Ezilo community, which was the scene of the incident today ... villagers were still bringing out corpses," Ebonyi state spokesman Onyekachi Eni told Reuters by telephone. "Fifty corpses were shown to us".

Violent disputes over land are common in Africa's most populous country because the majority of its 160 million people are subsistence farmers living in rural areas with few means of arbitrating disputes.

Hundreds of people are killed every year in such clashes, many going unreported because of a lack of reliable information about them.

State Commissioner of Police Adeola Adeniji said the divisional crime officer for the area was killed in the violence. "Mobile police have been sent there and the inspector general has directed more to come," Adeniji said.

Chioma Oke, an Ezilo who survived the clashes, said they started around 5 a.m.

"We heard sporadic gunshots and we began to run. They burned our houses. They said they were retaliating for an attack on them last year," she said.-Reuters