The cutting of ties between Ethiopia and Eritrea mark a dramatic reversal from 2018, when Abiy restored relations with Asmara after two decades of hostility, prompting joyous scenes as the border reopened and families separated for years were reunited.

The rapprochement helped earn the Ethiopian prime minister the Nobel Peace Prize in 2019.

The latest hostilities are the most serious since a peace agreement ended the devastating Tigray war in 2022. An African Union mediator previously estimated that about 600,000 people had died during that two-year conflict.

Last month, the TPLF joined six other armed movements, including the Fano militia from Amhara, to form an alliance whose stated objective is to remove Prime Minister Abiy Ahmed's government from power.

A pro-government militia commander fighting in Tigray told the BBC that Eritrean soldiers had been involved on the front lines.

The BBC has not independently verified the allegation.

The BBC is unable to report from Tigray and the internet has been cut, making it difficult to get reliable information from the region. It is not clear who was responsible for cutting communications.

In a rare response to the BBC before diplomatic relations were severed, Eritrea's Information Minister Yemane Gebremeskel denied that it was involved in the fighting in Tigray, which borders his country.

He told BBC Tigrinya that Ethiopia's governing Prosperity Party was blaming neighbouring countries to divert attention from conflicts and other problems within Ethiopia.

The two countries were allies during the 2020-2022 Tigray war, when Eritrean troops fought alongside Ethiopian federal forces against the TPLF.

But relations have deteriorated significantly since then, particularly over Ethiopia's push for direct access to the Red Sea.

Ethiopia lost its coastline when Eritrea became independent in 1993.

Abiy has repeatedly argued that access to the sea is essential to Ethiopia's long-term economic and security interests, while Eritrea has accused his government of harbouring ambitions over its ports.