The attackers, who took around 500 head of cattle, were "suspected Ethiopian Borana cattle rustlers", police said.
At least 12 people, including three children, were killed in two attacks in northern Kenya by cattle rustlers suspected to be from the Borana ethnic group, Kenyan police said Sunday.
The attacks on two villages in Kenya's Marsabit County near the border with Ethiopia were on cattle breeders from the Gabra ethnic group, long-time rivals of the Borana, police said in a statement.
"Five male Gabra adults were killed and three others were seriously injured" in one small village on Saturday evening, police said.
The attackers, who took around 500 head of cattle, were "suspected Ethiopian Borana cattle rustlers", the police said.
In the other attack, on a nearby village, four Gabra adults and three children between the ages of 13 and 15, including one girl, were killed, with four people injured.
The thieves took around 1,000 goats in the second attack, in which one of the raiders was killed.
Kenyan police units are "pursuing the criminals and holding ground to prevent further attacks and killings," the statement said.
Kenya started conducting its first national census since 2009 on Saturday, and the authorities said the exercise would continue in Marsabit.
The theft of livestock – and deadly attacks to carry out the crime – are common between cattle herding communities in northern Kenya.