A senior military commander with the Tigray forces told the BBC that the clashes near the town of Adwa involved heavy artillery and tanks.

Correspondents say the outcome of the fighting there could determine who controls the two roads leading to Mekelle, the capital of Tigray.

There have also been reports of clashes involving forces from neighbouring Eritrea near the border with the Afar region.

The Ethiopian military and its Eritrean allies recently took control of major towns in Tigray including Shire, Aksum and Adwa.