ADDIS ABABA, June 20 (CNN) - At least 200 civilians are believed to have been killed in Ethiopia's Oromia region by rebel group the Oromo Liberation Army (OLA) on Saturday, according to reports, a rights group and local officials. Most of the victims are from the Amhara ethnic group, a police officer said.

The attack on the town of Gimbi was connected to fighting between government forces and the OLA, according to a statement from the Ethiopian Human Rights Commission (EHRC). The EHRC told CNN Monday that the assault has left "scores of people injured, villages destroyed, and entire communities traumatized."

The OLA -- which last year aligned with Tigrayan rebel forces against Ethiopia's federal government in the country's protracted conflict -- has denied all the allegations. OLA spokesman Odaa Tarbii said Sunday that the "regime" of Ethiopia's Prime Minister Abiy Ahmed "is again blaming the OLA for atrocities committed by its own retreating fighters."

The rebel group has been designated as a terror organization by the Ethiopian government, and it is frequently accused of attacking civilians and targeting ethnic Amharas.

This incident is among the worst atrocities to hit the country since fighting broke out in Ethiopia's northern Tigray region in 2020, when Abiy's government and its allies from the neighboring Amhara region tried to suppress a rebellion by the Tigray People's Liberation Front (TPLF).

The TPLF dominated Ethiopia's government prior to Abiy's rise to power in 2018.

The ensuing civil war has seen both sides carry out atrocities, according to human rights groups, and risks splitting the ethnically diverse country. There is no suggestion TPLF was involved in Saturday's attack.

A local police officer involved in the response effort to Saturday's incident told CNN that an attack happened near Tole, a village within Gimbi, on Saturday, with the majority of the victims belonging to the Amhara ethnic group. The police officer spoke on the condition of anonymity as he was not authorized to speak on the matter.

The assault came days after heavy fighting between government security forces and the OLA in the area, he said.