"People fear for their security because the raiders are known," he said.
"They came to steal the animals and ... clashed with the herders who tried to block their mission."
The rival tribes have been fighting for land and water resources, which have been limited by a severe drought in the country's arid north.
The drought has shrivelled crops, killed cattle and left millions of Kenyans seeking emergency food aid.
Battles between nomadic tribes are believed to be common in the region but have become increasingly deadly due to the wide availability of modern weapons.