The rebel group was led by a traditional healer who claims to use magic to cure the sick and sought to control the road leading into South Sudan, said Omot. It is not an organised group and does not have a name, he added.
Several deadly clashes have erupted in Gambella in recent months, although Omot said last week’s incident was not connected to the previous attacks.
Gambella, which lies some 700 kilometres (430 miles) west of the capital Addis Ababa, is one of the most fertile and resource-rich areas of the country.
South Sudan was left awash with weapons after decades of war with north Sudan, from which it split in July last year.