Explainer-Why are Ethiopia and Eritrea on the brink of a possible war?

Longtime foes Ethiopia and Eritrea could be headed towards war, officials in northern Ethiopia and regional experts have warned.

A conflict would signal the death blow to a historic rapprochement for which Ethiopian Prime Minister Abiy Ahmed won the Nobel Peace Prize in 2019 and risk creating another humanitarian disaster in the troubled Horn of Africa region.

WHY HAVE FEARS OF WAR EMERGED?

The warnings stem from fresh instability in northern Ethiopia's Tigray region, where a civil war from 2020-2022 resulted in hundreds of thousands of deaths.

During the war, Eritrean forces crossed the border into Tigray to fight in support of Ethiopia's federal army against rebels led by the region's ruling party, the Tigray People's Liberation Front (TPLF).

But the peace deal signed in November 2022 drove a wedge between Ethiopia and Eritrea, which was not party to the negotiations. The TPLF, which runs Tigray's post-war interim administration with the blessing of the federal government, has since split.

A dissident faction seized the town of Adigrat this week. It accuses those in power of selling out Tigrayan interests, while the interim administration accuses the dissidents of collaborating with Eritrea.

Each side denies the other's allegations.

Experts say the standoff could lead to Ethiopia and Eritrea backing rival camps in Tigray and ultimately coming into direct conflict.

Eritrea ordered a nationwide military mobilisation in mid-February, according to a human rights group, and Ethiopia deployed troops toward the Eritrean border, diplomatic sources and Tigrayan officials told Reuters.

Eritrean and Ethiopian government spokespeople have not responded to requests for comment.

WHAT IS THE HISTORY OF ETHIOPIA-ERITREA RELATIONS?

The former Italian colony of Eritrea was annexed by Ethiopia in 1962. Rebel forces led by Isaias Afwerki waged a three-decade armed struggle that secured Eritrea's independence in 1993.

Independent Eritrea, which is still led by Isaias, initially enjoyed warm ties with Ethiopia, where Tigrayan-led rebels had overthrown longtime military ruler Mengistu Haile Mariam in 1991 with support from Isaias's rebels.

But clashes broke out in 1998 along the border over ownership of the disputed town of Badme, leading to a two-year war in which an estimated 80,000 people were killed.

The two countries remained formally at war - with all transport links cut and phone and postal services severed - until 2018 when President Isaias and newly-appointed Ethiopian prime minister Abiy agreed to normalise diplomatic relations and rebuild economic ties.

The deal led to the reunification of families who had not been able to communicate for two decades, direct flights between the capitals Addis Ababa and Asmara and pledges to jointly develop Eritrea's ports.

WHY DID TIES SOUR?

Relations took a turn toward the end of the Tigray war, when Ethiopia signed the Pretoria Agreement with the TPLF to end the fighting.

Analysts say Eritrea was unhappy at being excluded from the agreement which allowed the TPLF, with which it remains deeply hostile, to govern Tigray.

Some Eritrean troops have remained on Ethiopian soil since the end of the conflict, the United States has said, despite the deal calling for the withdrawal of all outside forces. Asmara has not directly addressed the accusation.

Eritrean officials have bristled at repeated public declarations by Abiy since 2023 that landlocked Ethiopia has a right to sea access - comments many in Eritrea, which lies on the Red Sea, view as an implicit threat of military action.

Last September, Ethiopian Airlines suspended flights to Eritrea - which had been a potent symbol of the countries' restored ties - after its bank account there was frozen.

The following month, Eritrea signed a security pact with Egypt and Somalia that was widely seen as aimed at countering Ethiopia's potential expansionist ambitions.

(Reporting by Aaron Ross; Editing by Ammu Kannampilly and Joe Bavier)