The Tigray People Liberation Front (TPLF) has accused Ethiopian and Eritrean forces of killings dozens of people including children during an air-strike.
Getachew Reda of the TPLF said the victims were displaced people who had fled to Adiyabo close to the border with Eritrea. It has not been possible to independently verify the attack.
There has been no comment from the governments in Addis Ababa and Asmara.
Humanitarian workers said an airstrike in the same area of Tigray last week killed at least six people.
The Ethiopian government has accused Tigrayans of keeping weapons in civilian areas.
In recent weeks there has been heavy fighting involving tens of thousands of troops with reports of heavy losses on all sides.
International efforts to push for a ceasefire are continuing.