Heavy fighting has been reported on several fronts in the northern Tigray region, in spite of the AU-led peace talks aimed at ending the long-drawn civil war.
The skirmishes near the town of Adwa involved heavy artillery and tanks, a top military commander with the Tigray forces confirmed.
Correspondents say the outcome of the fighting there could determine who controls the two roads leading to Mekelle, the capital of Tigray.
The talks holding in South Africa have been organised by the African Union (AU), which represents more than 50 countries on the continent.
Moussa Faki Mahamat, the chair of the AU Commission, said he had been encouraged “by the early demonstration of commitment … by the parties … to silence the guns”.
There have also been reports of fighting involving forces from neighbouring Eritrea near close to the Afar region.
The Ethiopian military and its Eritrean allies recently took control of major towns in Tigray including Shire, Aksum and Adwa.