Residents in Ethiopia’s largest federal state, Oromia, say dozens of civilians were killed in an attack by an armed group on Monday, the latest mass violence along ethnic lines that challenges one of Africa’s most populous countries.

Two residents of the restive Wollega region’s Horo Guduru area said an armed group from the ethnic Amhara community, known as Fano, targeted ethnic Oromos indiscriminately.

“Those Fano militia came in full force and killed everyone they found,” one witness told The Associated Press, speaking on condition of anonymity for fear of retaliation. He said he saw six fresh bodies in a graveyard. The fighters burned houses, looted cattle and threatened to come back and “finish us all,” he said.

Another witness said he saw around 20 bodies on Tuesday and said he believed that “many other bodies remain to be discovered.”

Both witnesses said the attack occurred a day after Oromia regional forces withdrew from the area. A spokesman for Ethiopia’s federal government, Legesse Tulu, hung up without answering questions. Oromia’s police chief did not respond.

On Thursday, Ethiopia’s Media Authority issued a warning to private media outlet Finfinnee Integrated Broadcast for reporting the killings and accused it of disseminating “fake and unconfirmed reports.”

Ethiopia has experienced widespread ethnic rivalry and conflict since Prime Minister Abiy Ahmed came to power in 2018.

The Fano militia was a major actor in Ethiopia’s Tigray conflict that erupted in the northern part of the country in November 2020. Fighting alongside Ethiopia’s military, they were implicated in some of the worst atrocities committed against ethnic Tigrayans.

But when that conflict calmed in recent months, many of the Fano’s leaders and members were targeted by Ethiopian authorities after the prime minister referred to them as an “irregular force.”

Previously, ethnic Amahras were targeted in the Wollega area where Monday’s killings occurred. In June, hundreds of ethnic Amharas were killed and local authorities blamed the Oromo Liberation Army. The armed group denied it and blamed government forces instead.