The armed militia from the Afar region attacked Andhufo town, the latest flare-up in a local boundary dispute that adds to broader tensions in Ethiopia.
An official in the Somali region, which stretches north to south along Ethiopia's eastern border, was quoted as saying that the Afar militia "massacred 20 civilians" in the town.
The official added that the people who were killed included women and people from the same family who died in the attack by the Afar militia.
It was also reported that some people were brutally killed and slaughtered at the same time, which left grief and pain to their relatives.
There was no immediate comment by Afar's government or the Somali regional state in Ethiopia. The ethnic conflict has been rising in the country since the start of the Tigray war.