Fighting between the Oromo and Somali peoples along the shared border between their two states occurred sporadically through 2017 but the situation intensified in September, leaving hundreds of people dead by a government estimate and displacing scores of others trying to flee the violence.
Statistics from the UN's International Organization for Migration (IOM) show that the conflict-related displacement is more widespread than previously known and one of the biggest seen by Ethiopia in recent years.
"Preliminary data from the latest round of the IOM Displacement Tracking Matrix conducted in November 2017 indicates that around 1 million persons have been displaced due to conflict along the Oromia-Somali regional border," dating back to at least 2015, said a report by the UN's Office for the Coordination of Humanitarian Affairs (OCHA).
An official with IOM's office in the capital Addis Ababa declined to comment further on the data, cited in the OCHA report dated January 23.
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Ethiopia is divided into ethnically demarcated federal states intended to give the country's many ethnic groups self-determination.
While Oromos and Somalis have lived side-by-side in each others' region, quarrels between the two ethnic groups over access to land and resources have occurred for years along the borders of their two states, Oromia and Somali.
The reasons for the conflict's sudden intensification last year remain unclear, but both sides accuse the other of carrying out atrocities and forcing people of the opposite ethnic group out of their respective states.