Ethiopia has warned Eritrea that it will take steps to protect its territory after accusing its northern neighbour of sending troops into the Tigray region, raising fresh fears of a military confrontation between the two countries following weeks of worsening relations.
The Ethiopian government has raised the matter with the United Nations Security Council, describing Eritrea's alleged actions as an invasion and insisting that it has the right to defend itself.
Eritrea has rejected the claims, instead accusing Ethiopia of provoking a conflict and pursuing plans to destabilise its government.
In a letter dated 8 October, Ethiopian Foreign Minister Gedion Timothewos accused Eritrean forces of advancing as far as 60km (37 miles) into Tigray.
He described the reported military movement as a violation of Ethiopia's sovereignty and called on members of the Security Council to understand and support the country's position.
The letter stated: "In this time of difficulty, when Ethiopia is left with no other option but to defend itself, we count on your understanding, support, and solidarity."
Timothewos also described the alleged incursion as a "blatant act of aggression that engages Ethiopia's inherent right to self-defence".
The allegations have added to an already tense situation in northern Ethiopia, where fighting erupted about two weeks ago between government forces and the Tigray People's Liberation Front (TPLF), the political group that controls the region.
Both sides have accused each other of violating the 2022 agreement that ended a two-year civil war in Tigray. Ethiopia has also accused Eritrea of supporting the TPLF, although Asmara has denied involvement in backing the group.
Eritrean Information Minister Yemane Gebremeskel has dismissed Ethiopia's accusations, arguing that his country is the one facing a threat from its neighbour.
Responding to the claims, Gebremeskel said Eritrea was facing "an unprovoked war of aggression" from Ethiopia.
On Friday, he described the accusations directed at Asmara as "duplicity in their most extreme forms".
In a post on X, the Eritrean official accused Ethiopia of attempting to remove his country's leadership by supporting individuals opposed to the government.
He said Ethiopia was "openly working to bring about regime change in Eritrea by providing shelter and support to certain mercenaries who claim to be opposition".
The diplomatic exchange comes as reports emerge of military action in Adigrat, a town in Tigray where Eritrean forces were reportedly targeted by Ethiopian drone strikes on Wednesday and Thursday.
The US-based conflict monitor Acled reported that "Eritrean troops and ammunition" in Adigrat were hit by "multiple drone strikes" overnight.
A resident who spoke to AFP news agency described the attacks as intense, saying "there were many, many drone strikes". The resident also reported that some Eritrean lorries had been destroyed.
A second witness told AFP that Eritrean troops appeared to be withdrawing northwards following the strikes.
No casualties have been independently verified so far, and the BBC has said it cannot report directly from Tigray. The reported troop movements and attacks therefore remain difficult to confirm independently.
The latest developments have heightened concerns that the fighting in Tigray could become part of a wider confrontation between Ethiopia and Eritrea, whose relationship has deteriorated sharply since they fought on the same side during the previous conflict.
During the two-year civil war, Eritrean forces supported Ethiopia's federal government in its fight against the TPLF. The former allies have since fallen out, with disagreements over Ethiopia's desire to secure access to a Red Sea port emerging as a major source of friction.
The dispute has contributed to the breakdown of diplomatic relations between the two neighbours, which severed ties last week.
Eritrea gained independence from Ethiopia in 1993 after a long struggle. Relations between the two countries were normalised in 2018 following the rise to power of Ethiopian Prime Minister Abiy Ahmed.
However, the improvement in relations has since given way to renewed hostility, driven in part by disagreements over regional security and Ethiopia's ambitions concerning access to the sea.
The latest crisis also follows months of mounting tension within Ethiopia and the formation of a new alliance of armed groups in September. The TPLF is among the groups included in the alliance, adding another layer of uncertainty to the country's security situation.
Last week, TPLF forces pulled out of Mekelle, the main city in Tigray, located about 115km (71 miles) south of Adigrat. Ethiopian government troops have since taken control of the city.
With fighting between Ethiopian forces and the TPLF continuing alongside the worsening dispute with Eritrea, the security situation in the north remains uncertain. Ethiopia maintains that Eritrea has violated its sovereignty and says it is prepared to defend itself, while Eritrea blames the Ethiopian leadership for fuelling the crisis.
The exchange of accusations, reported military movements and drone strikes have intensified fears that the dispute could extend beyond Tigray and threaten stability across the Horn of Africa.