Fighting broke out between the rebel Tigray People's Liberation Front (TPLF) and Ethiopian federal forces on September 23, sparking fears of a return to the devastating civil war of 2020-2022.

Over the weekend, the Ethiopian army and an allied Tigrayan militia entered the regional capital of Mekelle without a fight after the TPLF pulled out.

A commander with the militia told AFP his troops had reached Wukro town, roughly 50 kilometres (30 miles) north of the city, and on the main road leading to Eritrea in the north.

Sources said Eritrean troops were in Adigrat, around 40 kilometres (25 miles) by road south of the Eritrean border, with some headed south towards Mekelle.

Ethiopia has accused Eritrea of directly backing the Tigray rebels, with the added support of Sudan and Egypt, which all three countries deny.

"There have been Eritrean soldiers in Adigrat for the past four days, the population is very concerned," a local city official, speaking on condition of anonymity, told AFP.

An eyewitness also reported seeing troops "wearing Eritrean military uniforms" heading south along Adigrat's main road.

Another eyewitness said "Eritrean troops, loaded onto large trucks, patrol vehicles and other vehicles" were heading towards the town of Idaga Hamus, roughly 20 kilometres south of the city.

"They are passing through, carrying heavy weaponry," the witness added.

Long-standing tensions between Ethiopia and Eritrea have recently escalated with the two neighbouring countries severing diplomatic ties last week.

Eritrea, which shares a long border with the Tigray region, accuses landlocked Ethiopia of planning to invade its territory to gain direct access to the Red Sea.

The presidents of Egypt, Somalia, Sudan and Eritrea -- all of whom have difficult relations with Ethiopia -- met in the Egyptian coastal city of El-Alamein on Sunday.

They called for regional disputes to be resolved through "peaceful means", while stressing respect for international law and "non-interference in the internal affairs of states" in the Horn of Africa, according to a statement from the Egyptian presidency.

In a counter-offensive, Ethiopian forces have pushed deep into rebel-held territory, entering the regional capital, Mekelle, on Saturday without a fight, as TPLF leaders and troops abandoned the city.

Egypt and Ethiopia have been locked in a years-long dispute over the Grand Ethiopian Renaissance Dam, which Cairo fears could reduce its share of Nile waters.

Relations between the two countries deteriorated further this month after they expelled members of each other's diplomatic missions.

Egyptian Foreign Minister Badr Abdelatty told state-linked media on Sunday that Cairo has "absolutely nothing to do" with events in Ethiopia, describing the unrest as a "domestic crisis" rooted in ethnic and political divisions.

The TPLF ruled all of Ethiopia from 1991 until 2018, when it was marginalised with the rise of Prime Minister Abiy Ahmed, who hails from the Oromia region.

The tensions led to a civil war from 2020 to 2022 that killed more than 600,000 people, according to the African Union, making it one of the deadliest conflicts in the world in recent times.

The Pretoria peace agreement of 2022, brokered by African institutions and Washington, was never fully implemented but still helped keep a degree of peace until last year.