Eritrean troops have deployed in Ethiopia's northern Tigray region, multiple sources said Wednesday, threatening to turn an internal conflict into a wider regional war.
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 2020-2022 civil war.
Ethiopia accuses Eritrea of backing the rebels, and the two neighbours severed diplomatic ties last week.
The Ethiopian army has successfully pushed back the Tigrayan rebels with the help of local militias and entered the regional capital of Mekelle at the weekend without a fight as the TPLF abandoned the city.
Multiple sources told AFP that Eritrean troops have crossed the border and were positioned around Adigrat, some 115 kilometres (70 miles) north of Mekelle, and were pushing south.
Eritrea fears landlocked Ethiopia plans to invade to seize direct access to the Red Sea, and analysts say it wants to prevent the war reaching its territory.
"The Eritrean army has entered Tigray in uniform, equipped with heavy weaponry," said Gebreigziabher Beyene, commander of the Tigray Peace Force, a pro-government militia that has fought alongside the Ethiopian army.
"This force is being struck by drones," he said, adding Eritrea was "deliberately deploying its forces so that the fighting takes place inside Tigray rather than spilling into Eritrea".
In a statement on X, Eritrea's information minister, Yemane Meskel, did not deny that troops had crossed the border, but said Ethiopia's government was creating "a fallacious narrative of 'self-defence' to rationalise and camouflage its war of aggression".
In Adigrat, two eyewitnesses told AFP they saw Eritrean soldiers on the streets, heading south in lorries with heavy weaponry.
A local official, speaking to AFP on condition of anonymity, said the troops had been there for days and "the population is very concerned".
Conflict monitor ACLED said Eritrean troops had crossed the border at Zelambesa on Wednesday.
And it said Tigrayan rebel forces were "heavily present" around Wukro, a town along the same road that leads to the regional capital.
"Eritrean forces entered the war in Tigray to halt the Ethiopian government and allied forces from reaching the border and potentially fighting within Eritrea's territory," ACLED said in a briefing note.
Eritrea gained independence from Ethiopia in 1993 and the two sides fought a brutal border war between 1998 and 2000.
Relations improved markedly with the rise of Ethiopian Prime Minister Abiy Ahmed in 2018 and Eritrea even fought alongside Ethiopia during the 2020-2022 civil war against the TPLF.
But the relationship soon deteriorated, particularly over Ethiopia's persistent claims that it has a right to sea access.
Earlier this month, Ethiopia expelled 10 Eritrean diplomats and shut its embassy in Asmara, while Eritrea responded that it would "sever all diplomatic ties".
Britain and the United States were among countries warning their citizens to avoid travelling in northern Ethiopia.