Witnesses in Ethiopia said more than 200 people, mostly ethnic Amhara, had been killed in an attack in the country’s Oromia region.
Rebel group the Oromo Liberation Army was blamed for the outrage, but denied involvement.
It is one of the deadliest in recent memory as ethnic tensions continue in Africa’s second most populous country.
“I have counted 230 bodies. I am afraid this is the deadliest attack against civilians we have seen in our lifetime,” Abdul-Seid Tahir, a resident of Gimbi county, told the Associated Press after escaping the violence on Saturday.
“We are burying them in mass graves, and we are still collecting bodies. Federal army units have now arrived, but we fear that the attacks could continue if they leave.”
Another witness, who gave only his first name, Shambel over fears for his safety, said the local Amhara community was desperately seeking to be relocated somewhere else “before another round of mass killings happens”.
He said ethnic Amhara that moved to the area about 30 years ago in resettlement programmes were now being “killed like chickens”.
Both witnesses blamed the OLA for the attacks. The Oromia regional government also blamed the OLA, saying the rebels attacked “after being unable to resist the operations launched by (federal) security forces”.
OLA spokesman Odaa Tarbii denied the allegations.
“The attack you are referring to was committed by the regime’s military and local militia as they retreated from their camp in Gimbi following our recent offensive,” he said in a message to the AP.
“They escaped to an area called Tole, where they attacked the local population and destroyed their property as retaliation for their perceived support for the OLA. Our fighters had not even reached that area when the attacks took place.”
Ethiopia is experiencing widespread ethnic tensions in several regions, most of them over historical grievances and political tensions.
“I lost my 16-year-old daughter in the attack shot by a bullet from the gunmen,” one Amhara man said. He said rebels had blocked the main road.
Another man told AFP he had “personally helped bury 61 bodies on Sunday, with the total number of buried bodies on Sunday being 351 in total”.
“The intention of all these attacks is to force us to leave,” he said.
“Our houses and properties have been destroyed.
“I want to leave this area, go to my ancestral region … that at least would allow me to live in peace.”
Prime Minister Abiy Ahmed tweeted that his government had “zero tolerance for horrific acts claiming lives.”
“Attacks on innocent civilians and destruction of livelihoods by illegal and irregular forces is unacceptable,” he said.
Together, Amharas and Oromos make up the majority of Ethiopia’s 115 million people and Mr Ahmed’s government has previously accused the OLA of ethnic massacres.
The Amhara have been targeted frequently in regions like Oromia.