US Secretary of State Antony Blinken is greatly concerned about Ethiopia's military escalation and called for urgent negotiations over the crisis, a US State Department spokesperson has said.

The comments came hours after Ethiopian Prime Minister Abiy Ahmed appeared on the frontline with the national army.

"Secretary Blinken expressed grave concern about worrying signs of military escalation in Ethiopia and emphasised the need to urgently move to negotiations," Ned Price said in a statement.

Mr Price released the statement after a phone call between Kenya's President Uhuru Kenyatta and Mr Blinken.

Yesterday, Ethiopia's state-affiliated Fana Broadcasting reported that Mr Abiy was on the frontline with the army fighting rebellious Tigrayan forces in the northeastern Afar region.

The 2019 Nobel Peace Prize winner posted the same video on his Twitter account.

Mr Abiy's government has been fighting Tigrayan forces for more than a year, in a conflict that has killed thousands and displaced millions in Africa's second-most populous nation.

This week he announced he would start leading operations against the Tigray People's Liberation Front, which once dominated national politics but has been locked in a gruesome war with his government for the past year.

The TPLF, he added, "is destabilising our country beyond its region".

The conflict has killed thousands and displaced millions in Africa's second-most populous nation.

On Wednesday state-affiliated media announced Mr Abiy had handed over regular duties to his deputy.

His move came after the TPLF reported major territorial gains, claiming this week to have seized a town just 220 kilometres from the capital, Addis Ababa.

The TPLF has aligned itself with other armed groups including the Oromo Liberation Army, which is active in the Oromia region surrounding the city.

War in Tigray: How did it start and can it be resolved?

Earlier this week, the Department of Foreign Affairs advised Irish citizens in Ethiopia to leave the country immediately.

Minister for Foreign Affairs Simon Coveney said around 80 Irish citizens in Ethiopia have been advised it would be prudent to leave the country due to an escalation in the political situation in the conflict-ridden country.

Meanwhile, the Ethiopian government has informed Ireland's embassy in Addis Ababa that four of the six Irish diplomats serving at the embassy must leave the country within one week.

Ireland's ambassador and one other diplomat have been permitted to stay.