At least 11 people were killed and more than 20 others wounded by members of the rebel Oromo Liberation Front (OLF) in Keremu district in east Wellega zone of Oromia Regional State.
Eyewitnesses said OLF-Shene shot dead 11 civilians Thursday afternoon at a place called Nechelo area where their bodies remained uncollected until late Friday.
Hundreds of residents in the district have displaced the area for fear of another round of attacks.
Recently, the National Defense Forces had cleared the area from OLF-Shene fighters but the latest attack came after the national army abandoned the district.
The Oromia Police Officials confirmed the killing but fell short to give detailed information.