Eritrean troops have deployed in recent days around the town of Adigrat in Ethiopia's northern Tigray region, according to a local official and residents, raising fears that a two-week internal conflict could grow into a war between neighbouring states. Adigrat lies about 115 kilometres (70 miles) north of the regional capital Mekelle, on the road to the Eritrean border.

Fighting broke out on September 23 between Ethiopian federal forces and the rebel Tigray People's Liberation Front (TPLF). The Ethiopian army, backed by local militias, has pushed the TPLF back and entered Mekelle at the weekend without a fight after the group abandoned the city. Multiple sources told AFP that Eritrean soldiers were in Adigrat and moving south. Two eyewitnesses described troops on large trucks and patrol vehicles carrying heavy weaponry, and a local official said the population was "very concerned". Gebreigziabher Beyene, commander of the pro-government Tigray Peace Force, said the Eritrean army had entered in uniform and accused it of deliberately fighting inside Tigray rather than on its own soil. Insecurity has also been reported elsewhere: a resident of Adwa, west of Mekelle, said drone strikes over the weekend hit hotels and killed several civilians.

The deployment comes on top of a sharp deterioration in relations. Ethiopia accuses Eritrea of backing the rebels. Earlier this month Addis Ababa expelled 10 Eritrean diplomats and closed its embassy in Asmara, and Eritrea responded that it would sever all diplomatic ties. Eritrea became independent from Ethiopia in 1993, and the two countries fought a bloody border war from 1998 to 2000. Ties improved after Abiy Ahmed became Ethiopia's prime minister in 2018, and Eritrea fought alongside Ethiopian forces against the TPLF in the 2020–2022 civil war, which some analysts consider the deadliest conflict of the 21st century so far, with an estimated 600,000 deaths. Since then the relationship has soured, and Eritrea fears that landlocked Ethiopia intends to seize direct access to the Red Sea by force.

Analysts say Eritrea's move is largely defensive. Kjetil Tronvoll of Oslo New University College told AFP that Eritrea considers it essential to keep a buffer zone in northern Tigray and to meet the Ethiopian army on Tigrayan soil. There were also fears this week that the TPLF could retreat into Eritrea, which could give Ethiopia a pretext to invade. Abiy told parliament on Monday that Ethiopia's modernisation cannot succeed without sea access, words Eritrea may read as a threat. At the weekend, Eritrean President Isaias Afewerki met the presidents of Egypt, Sudan and Somalia, who declared that the Red Sea's governance is a matter for coastal states alone, a message widely seen as aimed at Ethiopia.

The stakes extend beyond the two countries. The Red Sea region already faces war in Sudan, instability in Somalia and conflict around Yemen's Bab al-Mandab strait, and in normal times a third of global container traffic passes through the waterway. A commentary in the Swiss daily NZZ argues that international reaction has been too weak: the United States and European Union have urged restraint and de-escalation, while the African Union, headquartered in Addis Ababa, has traditionally been cautious with its host. The commentary notes that the EU released 140 million euros in development aid to Ethiopia only in April, and points to economic leverage as a possible tool for pressing for an end to the fighting.