Ethiopia’s government said its forces killed at least 550 fighters loyal to the ruling party of the northern Tigray region, as the African Union called for an immediate cease-fire.

Fighting is continuing in Tigray a week after federal troops began an incursion into the region in retaliation for an attack on one of its army camps in the region. Prime Minister Abiy Ahmed blamed the ruling Tigray People’s Liberation Front for the raid — a claim the TPLF denies.

It’s unclear whether those killed are part of the TPLF’s special forces or militia fighters supporting the party, said Redwan Hussein, state minister for foreign affairs and spokesman for the newly established State of Emergency task force. The number of casualties suffered by Ethiopia’s army are still being counted, he said.

African Union Chairman Moussa Faki Mahamat said late Tuesday he’s concerned by the escalating tensions in Ethiopia and urged all parties to begin talks to find a peaceful solution to the crisis. “The chairperson appeals for the immediate cessation of hostilities and calls on parties to respect human rights and ensure the protection of civilians,” Faki said in a statement.