Federal troops' 10-day push against the northern state has sent refugees flooding into Sudan and raised fears it may suck in Eritrea or weaken an African force opposing Islamist militants in Somalia if Ethiopia diverts troops from there.

It may also blemish the reputation of Prime Minister Abiy Ahmed, who won a Nobel Peace Prize for a 2018 peace pact with Eritrea and had won plaudits for opening Ethiopia's economy and easing a repressive political system.

Abiy accuses the Tigray People's Liberation Front (TPLF), which rules the mountainous region of more than five million people, of treason and terrorism. They say he has systematically persecuted Tigrayans since taking office in April 2018.

The conflict began last week when Abiy says the TPLF attacked a military base, since when his army has been carrying out air strikes and ground combat which the government says has "liberated" west Tigray.

Abiy, who comes from Ethiopia's largest ethnic group the Oromo, said parliament had named former Addis Ababa university professor and deputy minister for science and higher education Mulu Nega, 52, as chief executive of Tigray.

"The Chief Executive will recruit and appoint heads to lead executive organs of the regional state from political parties legally operating in the region," he tweeted.

Current Tigray leader Debretsion Gebremichael, who won a local election in September despite central government orders to cancel it, has been formally accused along with other TPLF officials of treason, armed rebellion and terrorism.

They say their region has been invaded.

Abiy's opening of political space since taking office in 2018 has exposed ethnic fractures in Africa's second most populous nation of 115 million people. Before the Tigray flare-up, clashes killed hundreds and uprooted hundreds of thousands.

Communications in Tigray are cut and media have been barred, but security sources have told Reuters hundreds of combatants have been killed on both sides.

Both sides have accused each other of harming civilians.

Rights group Amnesty International said on Thursday that scores and possibly hundreds of civilians were stabbed and hacked to death in the region on November 9, citing witnesses who blamed the TPLF. Debretsion denied that in comments to Reuters.

More than 11,000 Ethiopian refugees - half of them children - have gone to Sudan since fighting started and aid agencies say the situation in Tigray is becoming dire.

Ethiopia's national army is one of Africa's largest and highest-trained. But its best fighters are from Tigray and much of its hardware is also there, under the Northern Command.

Australian Associated Press