ADDIS ABABA, Ethiopia (AP) — Ethiopian officials said Monday an unspecified number of civilians including children have been “massacred” in what they described as a terror attack on Sunday evening in the far western part of the Oromia region.

Ethiopia’s prime minister, Abiy Ahmed, in a Facebook post denounced the killing of people based on identity. “Ethiopia’s enemies are vowing either to rule the country or ruin it, and they are doing everything they can to achieve this,” he said. “One of their tactics is to arm civilians and carry out barbaric attacks based on identity. (For me) this is heartbreaking.”

Security forces have been deployed to the area and “have started taking measures,” he said.

It was not immediately clear how many people were killed. The Ethiopian Human Rights Commission cited an official figure of 32 dead but said preliminary evidence it obtained “indicate the number is very likely to exceed that tally.”

Attackers numbered up to 60 and they arrived after federal soldiers withdrew from the area earlier Sunday, the commission said in a statement, citing sources. The attackers targeted ethnic Amharas, it said: “They were dragged from their homes and taken to a school, where they were killed.”

The commission urged the federal government to “shed light on the reasons behind the military’s withdrawal from an area long known to be vulnerable to attacks” and to make sure civilians are protected.

“A brutal terror attack carried out yesterday in West Wollega’s Guliso area has caused the loss of civilian lives,” the Oromia region’s communications office said in a statement. “Women, children, the elderly and the youth were subjected to killings, abductions and injuries.”

The region borders South Sudan and is a few hundred kilometers west of Ethiopia's capital, Addis Ababa.

Getachew Balcha, the region’s spokesman, accused a rebel group, the Oromo Liberation Army, of carrying out the attacks, saying they were aimed at creating havoc and putting psychological pressure on citizens.

“The armed group gathered 200 people for a meeting around 5 p.m., and then started shooting at them. Several people were killed as a result,” the Amhara region’s affiliated broadcaster, Amhara Mass Media Agency, quoted one survivor as saying. The survivor said a school and some 120 houses were burned.

Amharas are the second most populous ethnic group in Ethiopia after Oromos. They also have been targeted by gunmen in the Western Benishangul Gumuz and Southern regions in recent weeks, leaving several dozen dead.

“The government has failed in its duty to protect the safety of citizens,” Dessalegn Chanie, a senior member of the opposition National Movement of Amhara party, told The Associated Press, adding that Ethiopia’s language-based federal system is the main cause for the killings: “Ethnic Amharas residing outside of the Amhara region are being labeled as outsiders and are exposed to repeated attacks.”

Under the system, Afan Oromo speakers generally live in Oromia, Amharic speakers generally live in the Amhara region and so on. The structure gives locals more say in local affairs.

The Oromo Liberation Army hasn’t commented on the attack allegations. It has denied similar reports in the past.

The rebel group, a splinter wing of the Oromo Liberation Front party, has used the western Oromia region as its base since its members returned to Ethiopia after Abiy shortly after taking office in 2018 invited once-banned groups to return home from exile.