Responsible Statecraft has reported:

Ethiopia has accused Eritrean forces of advancing as far as 38 miles into its northern Tigray region and says it will defend itself, while Eritrea has called the accusation a “declaration of war.” The exchange comes amid reports of Ethiopian drone strikes near Adirgat, a renewed rebellion inside Ethiopia and increasing regional alignments that could draw other countries into a conflict between the neighbours.

On Friday, Ethiopian Foreign Minister Gedion Timothewos wrote to the United Nations Security Council, invoking Article 51 of the U.N. Charter. He said Eritrean troops had entered as far as 38 miles into Tigray and stated that Ethiopia would defend itself against the incursion.

Eritrean Foreign Minister Osman Saleh sent a separate letter to the Security Council on Saturday, describing Ethiopia’s accusations as a “declaration of war.” Saleh cited a statement he attributed to Ethiopia’s deputy chief of staff, Gen. Abebaw Tadesse, who, the letter said, stated on September 27 that the “ultimate objective of the war [in Tigray] was to invade Assab.” Assab is a city on Eritrea’s Red Sea coast.

Ethiopian forces reportedly used drones against Eritrean forces near Adirgat on Wednesday and Thursday. An unnamed security source told AFP that between 5,000 and 8,000 Eritrean troops are deployed in Tigray.

The present tensions follow years of conflict and unresolved disputes between the countries. In 2020, Ethiopia’s federal government, led by Prime Minister Abiy Ahmed, fought the Tigray People’s Liberation Front (TPLF), a movement that had dominated Ethiopian politics for nearly three decades.

After Abiy took power in 2018, the TPLF withdrew to its stronghold in Tigray. Tensions rose as it refused to join Abiy’s new ruling party, held regional elections in defiance of the federal government and, according to Abiy, attacked a federal army base.

Eritrea fought alongside Ethiopian forces during the first Tigray war. The conflict ended in 2022 with the Pretoria agreement, a ceasefire that left major questions unresolved, including disarmament, disputed territory and the withdrawal of forces that were neither federal nor part of Ethiopia’s National Defense Force. Eritrea was not a party to the agreement.

The trust that briefly developed between the neighbouring governments has since eroded. Ethiopia lost access to the sea when Eritrea became independent in 1993. Abiy has described the loss of the Eritrean port of Assab as a mistake “that will be corrected tomorrow.” Ethiopian officials have often said the country seeks sea access through peace and dialogue, while Eritrea says its larger neighbour intends to use force, as reflected in Saleh’s letter to the U.N.

Ethiopia is also contending with an internal rebellion. On September 20, the TPLF and six other armed groups announced the Ethiopian Peoples’ Alliance for Survival. The alliance says it aims to remove Abiy and install a transitional government. Its members include the Fano militias in the Amhara region and the Oromo Liberation Army, groups behind insurgencies in Ethiopia’s two largest and most populous regions.

Addis Ababa says Eritrea finances and directs the rebels. Asmara says Ethiopia has been planning to invade Eritrea for three years. The source article says public evidence supports both accounts.

Eritrea has begun opening channels and coordinating with the TPLF, a significant shift given the two sides’ past conflicts. They fought in the first Tigray war and earlier in the devastating 1998-2000 border war, when the TPLF still dominated Ethiopian politics. Eritrea, a small country facing a much larger neighbour, is seeking a buffer by keeping the TPLF in that role. While the TPLF remains armed, Ethiopia’s army cannot deploy cleanly to the Eritrean border.

Eritrea has also cultivated Egypt and Sudan’s army as allies. Both have grievances with Ethiopia over its construction of the Grand Ethiopian Renaissance Dam. Sudan also accuses Ethiopia of supporting the Rapid Support Forces, which are fighting Sudan’s military.

For Addis Ababa, the ties among Eritrea, the TPLF, Egypt and Sudan look like encirclement. Abiy recently dismissed the threat, saying his government did not have “an iota of fear” about it.

Eritrean troops have been present in Ethiopia before the latest reported advance. The Pretoria agreement and its follow-up, the Nairobi declaration, linked the disarmament of Tigrayan forces to the withdrawal of “foreign and non-ENDF [Ethiopian National Defense Force] forces.” Eritrean troops left larger towns but remained in contested border pockets. Asked about their presence in 2023, Eritrean President Isaias Afwerki called the question “nonsense.” The reported advance would deepen that presence and gives Addis Ababa grounds to say Eritrean forces are deep inside its territory and that Ethiopia must fight back in self-defence.

Diplomatic ties have also deteriorated. Ethiopia and Eritrea severed relations on October 1, while Ethiopia and Egypt expelled each other’s diplomats. Ethiopia’s military chief of staff, Field Marshal Birhanu Jula, accused “Shaebia,” a widely used term for Eritrea’s government, along with “Sudan, Egypt, and powers beyond” of supporting the TPLF’s renewed military insurgency.

On October 4, Egypt hosted the leaders of Eritrea, Somalia and Sudan at El Alamein, on Egypt’s Mediterranean coast. They declared that governance of the Red Sea belongs to coastal states, a position directed at landlocked Ethiopia. Reuters, citing Egyptian security officials, reported that the four countries agreed to co-ordinate military and intelligence efforts if the conflict spills beyond Ethiopia’s borders. A war between Asmara and Addis Ababa could therefore involve other countries.

Ethiopia’s recent military gains may increase the risk of escalation. Government-allied units recaptured Mekelle, Tigray’s capital, on October 4, and Ethiopian Airlines resumed flights to the city on Sunday. Getachew Reda, a former Tigray leader who now advises Abiy, greeted supporters at the airport on Sunday and promised “visible change.” Addis Ababa could conclude that its military momentum offers a chance to address both its security concerns about Eritrea and its lack of a coastline by taking the fight north.

There are also substantial reasons for Ethiopia to hold back. The TPLF has withdrawn from Mekelle, but its command remains intact and has not collapsed. Other alliance members, including the Fano in Amhara and the Oromo Liberation Army in Oromia, remain committed to fighting.

Ethiopia’s dependence on a single highway to Djibouti for most of its imports adds another vulnerability. The TPLF’s recent advance into the Afar region, where the corridor lies, demonstrated how exposed the route is and how much leverage the rebels could gain against the federal government. With half the country in revolt, a push into Eritrea aimed at regime change or annexation would be a major gamble.

International efforts have so far offered limited reassurance. The African Union is headquartered in Addis Ababa and has long faced accusations of going soft on its host country. The source article attributes much of the failure to resolve Pretoria agreement issues to the AU’s lethargy and systemic inaction.

Washington may be better positioned to mediate. Ethiopia has long been considered the United States’ most important partner in the Horn of Africa, and Washington is now warming to Eritrea. U.S. Ambassador Ervin Massinga had travelled between Mekelle and Addis Ababa and engaged the TPLF. As the Tigray insurgency accelerated, however, he blamed the group’s “poor decision to launch a large-scale offensive.” Whether the U.S. can still help resolve tensions between Ethiopia and Eritrea remains uncertain, and the source article says Washington appears unprepared for what may come.

Days before fighting resumed, the U.S. allowed the sanctions regime tied to the previous Tigray war to lapse, removing Eritrean officials and entities from the list. It had already eased restrictions on arms sales to Addis Ababa. On September 30, while fighting was under way, Boeing signed a $5 billion aircraft deal with Ethiopian Airlines.

Washington has backed Abiy’s vision of Addis Ababa becoming Africa’s Dubai, alongside a planned $12.5 billion airport at Bishoftu that is intended to be among the world’s largest. Ethiopia is also seeking business ties with Washington as it pursues an ambitious economic transformation. A country sliding into civil war while facing a simultaneous interstate war with its northern neighbour could soon have little capacity to buy or build.