In two days of attacks in Oromia region, more than 60 people were killed, more than 70 others wounded, as well as homes and cattle looted. AFP
The Ethiopian Human Rights Commission said it was "highly concerned" by the attacks in the western region's Amuru district from August 30 to 31.
The EHRC said it had learnt "from locals and government officials that in two days of attacks, more than 60 people were killed, more than 70 others wounded, as well as homes and cattle looted".
It said the attacks also displaced 20,000 people.
The killings occurred after the Oromo Liberation Army, a rebel group, killed three ethnic Amharas in Abora city, it said.
Armed men from nearby areas, as well as some from the neighbouring Amhara region, responded by attacking ethnic Oromos in almost a dozen villages.
"The attack was carried out on civilians in Amuru district after security forces who were deployed in the area moved to another location," the monitor said.
Two survivors from one village told AFP last week the attackers were members of a militia based in the Amhara region.
The OLA said the Amhara Fano militia staged the attack.
Regional authorities blamed the OLA, which it and federal forces have been fighting since 2018 and which Addis Ababa has designated a "terrorist" group.
Officials have blamed the OLA for a number of massacres targeting Amharas, Ethiopia's second largest ethnic group, although the rebels have denied responsibility.
In June and July, gunmen massacred several hundred people, mostly Amhara, in two remote areas in the west of Oromia.
In August last year, more than 210 people were killed over several days of ethnic violence in Oromia region, the EHRC has said. It said OLA-linked gunmen killed more than 150 people, then more than 60 lost their lives in reprisal attacks.