A Prime Minister's office spokesperson, Billene Seyoum stated Thursday "Per data I have received from the Oromiya region yesterday, the number of victims identified so far rests at 338."
On June 18 gunmen killed at least 200 people in the Gimbi district of Western Wollega Zone, according to two local witnesses who helped bury the bodies.
Ethnic Oromos, Amharas and Gumuz were among the victims, Seyoum said, accusing the Oromo Liberation Army (OLA) of responsibility.
The OLA has previously denied involvement and called for independent investigation.
The outlawed Oromo force is connected to the Oromo Liberation Front, a formerly banned opposition group that returned from exile after Prime Minister Abiy Ahmed took office in 2018.
A United Nations-appointed International Commission of Human Rights Experts on Ethiopia called for experienced investigators and other logistical support so it can examine incidents such as the latest attack in Oromiya.
"The most recent events in western Oromiya clearly fall within the mandate of the commission and require immediate, urgent and thorough investigations," Betty Murungi, chair of the commission, told member states at a briefing in Geneva on Thursday.
Ethiopian federal troops went to war with rebellious Tigrayan forces in November 2020. Since then, Reuters has reported atrocities by all sides, including executions and sexual violence, which the belligerents have denied.