An attack by gunmen in Ethiopia's western Oromiya region left at least 260 civilians dead, Reuters reported on Monday citing two residents who gave detailed accounts of how they had taken part in burying corpses in mass graves.

One resident gave a figure of 260 dead, the other said 320.

Authorities have not confirmed the death toll. 

Earlier, Prime Minister Abiy Ahmed condemned what he described as "horrific acts" in Oromiya, without giving details.  

(With input from Reuters)