The attack took place on the border with Somalia and had been coordinated by the Islamist group.
According to the terror group's radio station it was a "well-planned attack which targeted Christian members in Mandera".
In recent years, attacks on Christians have increased. Last April almost 150 people were killed in an attack on a university and in December Muslims protected their Christian counterparts in an attack on a public bus.
A Kenyan government spokesperson told The Times that security agencies had information that an attack was planned "but there was no actual and accurate specific intelligence."
The killers escaped across the border in Somalia.
