Ethiopians have been urged to “save themselves” after Prime Minister Abiy Ahmed gave Tigrayan forces 72 hours to surrender or he would surround a regional capital with tanks.

But the Tigray People’s Liberation Front, which is refusing to surrender its rule of the northern region, said its forces were digging trenches and standing firm, prompting fears of a looming deadly conflict.

“We urge you to surrender peacefully within 72 hours, recognising that you are at the point of no return,” Mr Abiy said in a message posted on Twitter on Sunday night (local time).

Tigrayan forces could not immediately be reached for comment.

A military spokesman said earlier that advancing Ethiopian troops planned to surround the regional capital of Mekelle with tanks and might shell the city to force surrender.

“The next phases are the decisive part of the operation, which is to encircle Mekelle using tanks,” military spokesperson Colonel Dejene Tsegaye told the state-run Ethiopia Broadcasting Corporation.

“We want to send a message to the public in Mekelle to save yourselves from any artillery attacks and free yourselves from the junta … After that, there will be no mercy.”

TPLF leader Debretsion Gebremichael told Reuters by text message that his forces were resisting a push from the south while also fighting near the northern town of Adigrat after it fell to federal troops.

Mr Abiy’s federal troops have taken a string of towns during aerial bombardments and ground fighting. They are aiming for Mekelle, a highland city of about 500,000 people where the rebels are based.

The conflict that erupted on November 4 has killed hundreds, possibly thousands, and sent more than 30,000 refugees into neighbouring Sudan.

Rockets have been fired by rebels into neighbouring Amhara region and across the border into the nation of Eritrea.

Foreign nations have urged talks, but Mr Abiy has pressed on with the offensive.

In his statement on Sunday, Mr Abiy said that during what he terms a law enforcement operation “all the necessary precautionary measures have been taken to ensure that civilians are not harmed”.

Referring to the TPLF, he said that “all that the clique is left with is the fort that they have set up in Mekelle and empty pride”.

He said the people of Tigray had had enough of what he said was TPLF violence against them. He appealed to the people of Mekelle to stand with the federal troops in “bringing this treasonous group” to justice.

-with AAP