The clashes follow long-standing tensions between the central government and Tigray leadersImage caption: The clashes follow long-standing tensions between the central government and Tigray leaders
The leader of the Tigray region in northern Ethiopia has called on the African Union to intervene to stop the country from "spiralling into civil war".
In a televised statement, Debretsion Gebremichael said Tigray would continue to defend itself until the federal government agreed to negotiate.
But the Ethiopian Prime Minister, Abiy Ahmed, said consistent transgressions by Tigray's regional leaders had pushed him to take military action.
Reports from the neighbouring Amhara region say 100 federal soldiers were being treated for wounds.
Earlier, Mr Abiy without explanation sacked his army chief, head of intelligence and foreign minister.
The new army chief Berhanu Jula said federal troops had captured four towns in western Tigray.