Addis Ababa-UN chief Antonio Guterres called on Friday for the immediate de-escalation of tensions in northern Ethiopia where fighting has erupted between federal forces and troops in the Tigray region.

Long-running tensions erupted into armed conflict this week between Addis Ababa and the Tigray region, whose leaders effectively ruled the country for three decades until Prime Minister Abiy Ahmed came to power.    “I’m deeply alarmed over the situation in the Tigray region of Ethiopia. The stability of Ethiopia is important for the entire Horn of Africa region,” Guterres wrote on Twitter.

“I call for an immediate de-escalation of tensions and a peaceful resolution to the dispute.”

Abiy, the winner of last year’s Nobel Peace Prize, announced Wednesday that he had ordered military operations in Tigray in response to an “attack” by the region’s ruling party, the Tigray People’s Liberation Front (TPLF), on a military camp there. 

“Our country has entered into a war it didn’t anticipate. This war is shameful, it is senseless,” Ethiopia’s deputy army chief Berhanu Jula told a press conference Thursday.

The TPLF denies the attack occurred and accuses Abiy of concocting the story to justify deploying the military against the party.

Tigray president Debretsion Gebremichael said Thursday that fighting was taking place in western Tigray, and that federal troops were gathering on the border in neighbouring Amhara and Afar regions.

A diplomatic source said there were probably casualties on both sides after heavy fighting and artillery shelling Thursday on one of the main roads linking Tigray to neighbouring Amhara region.

An aid worker, speaking on condition of anonymity, said 25 wounded soldiers had been admitted to a health centre in Amhara on Thursday, without specifying which side they were from.

Internet and phone connections in Tigray have been cut, making any tolls difficult to verify.