A Kenyan official says four more children have been killed by an explosive device that went off in a field where they grazing livestock.

Mandera Governor Ali Roba is blaming devices that Britain might have planted during its colonial occupation of Kenya for the deaths on Saturday. He asked security agents to clear the fields of any devices from before Kenya gained independence in 1963.

Five children between the ages of 12 and 17 were killed in the same area of northern Kenya on Dec. 20 while playing with an explosive device they found while grazing livestock.

Many children living in the arid and semi-arid regions of Kenya often tend to their family's livestock after school. Some are forced to drop out of school to do so.