A diplomatic source told AFP Friday there had already been at least one credible report this week of an air strike near the regional capital, Mekele, targeting military assets.

Speaking on state television Friday in Tigrinya, the language of Tigray, Abiy indicated more were on the way.

"There will be air strikes. These air strikes aren't aimed at civilians but rather at targets stored by this dangerous group," he said, referring to hardware held by Tigray's ruling party.

Abiy, the winner of last year's Nobel Peace Prize, announced Wednesday he had ordered military operations in Tigray in response to an "attack" on a military camp by the Tigray People's Liberation Front (TPLF).

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

The military escalation came after months of rising political tensions between the federal government and Tigray, whose leaders effectively ruled the country for three decades until Abiy came to power in 2018.

UN chief Antonio Guterres called Friday for the immediate de-escalation of tensions amid reports of heavy shelling and troop movements, while observers warned an all-out war between the two powerful armies could be long and bloody.

Abiy wrote on Twitter Friday that the military operations "have clear, limited and achievable objectives -- to restore the rule of law and the constitutional order."