The violence in Oromia is a thorny challenge for Mr. Abiy, who is himself a member of the Oromo ethnic group. He was catapulted to power in 2018 in a wave of demonstrations in the region against the previous government. Those protests were stoked by Oromos who felt that they had been sidelined politically and economically, even though they were Ethiopia’s largest ethnic group.
But as Mr. Abiy, who was born in Oromia, sought to centralize his authority, observers said that his actions isolated many in the region, particularly those who had been championing more autonomy. Mr. Abiy’s government responded by cracking down on protests, closing down offices linked to Oromo political groups and arresting leading activists, including Jawar Mohammed, a prominent critic of the prime minister.
The clampdown pushed many young Oromo nationalists to “switch from peaceful protests and registered political parties to the rebellion” fronted by the Oromo Liberation Army, said William Davison, a senior Ethiopia analyst at the International Crisis Group.
The new allegation by Mr. Abiy that the Oromo Liberation Army committed another massacre this week was backed up by the state-appointed Ethiopian Human Rights Commission, which said that the militant group had killed ethnic Amhara civilians in two villages in the Qellem Wollega area, about 370 miles west of the capital, Addis Ababa.
Neither Mr. Abiy nor the commission provided a death toll, but Hone Mandefro, advocacy director for the Amhara Association of America, said that more than 300 people had been killed, with 120 buried on Tuesday in one of the villages. Dozens more were abducted during the attack, he said, and their whereabouts remain unknown.
The Oromo Liberation Army, in a Twitter post on Tuesday, instead put the blame for the attacks on militias aligned with Mr. Abiy’s government.
Their claim was bolstered late on Tuesday night, when a lawmaker from Mr. Abiy’s governing Prosperity Party disputed the official account, saying on a live video on Facebook that senior government officials in Oromia, including the region’s leader and police commissioner, had helped organize the attacks.
The Prosperity Party lawmaker, Hangaasa Ahmed Ibraahim, called on Mr. Abiy to take action against the leadership in Oromia and to protect civilians.
“We are tired of seeing rest-in-peace and condolence statements,” he said in a broadcast that stretched for nearly two hours, in which he urged Mr. Abiy: “Do your work to lead the country.”
The head of communications for the Oromia region did not respond to requests for comment.
Phone networks in the remote villages remained down on Wednesday, making it hard to reach residents.
But Tolasa Raga, head of the Hawa Galan hospital in the town of Gaba Robi, about 10 miles from where the killings took place, said that the hospital had received 35 injured people.
“They all sustained bullet wounds, and some are in critical condition,” Mr. Raga said in a phone interview.
Mohammed Sied, a 45-year-old farmer from Gaba Robi, said that he and other villagers had gathered 30 bodies in front of a mosque in one of the villages and buried them.
The latest killings come on the heels of another massacre, in western Oromia in June, when armed assailants stormed the village of Tole, which also has a majority Amhara population, and began indiscriminately shooting at civilians. The attack left hundreds dead and at least 2,000 others fleeing their homes, according to the United Nations Office of the High Commissioner for Human Rights.
Ethiopia is also grappling with one of the most severe droughts to hit the country in four decades, leaving millions of people hungry. Last week, UNICEF said that child marriage in Ethiopia had more than doubled in the past year in the regions worst hit by the drought because parents were marrying off their young girls for financial reasons.