Abiy on Sunday called on the TPLF to surrender peacefully within three days, saying they were 'at a point of no return'
The leader of Ethiopia's dissident Tigray region said on Monday that his people were "ready to die" defending their homeland, rejecting Prime Minister Abiy Ahmed's ultimatum that they surrender within 72 hours.
Abiy launched a military campaign against the Tigray People's Liberation Front (TPLF) on November 4, accusing it of attacking two federal military camps in the northern region, as well as defying and seeking to destabilise his government.
The federal army says its forces are within 60 kilometres of Mekele, the Tigrayan capital and seat of the TPLF, ahead of a threatened all-out bombardment of the city of half a million people.
Abiy -- last year's Nobel Peace Prize winner -- on Sunday called on the TPLF to surrender peacefully within three days, saying they were "at a point of no return."
But the TPLF's leader Debretsion Gebremichael said Abiy was trying to cover for setbacks his army had suffered against Tigrayan forces, and was issuing threats to buy time.
"He doesn't understand who we are. We are people of principle and ready to die in defence of our right to administer our region," Debretsion told AFP via WhatsApp.
A communications blackout in the region has made claims from both sides difficult to verify.
'No mercy' threat
Brigadier General Tesfaye Ayalew, as quoted by state-affiliated Fana Broadcasting Corporate on Monday, said that federal troops were "marching into Mekele" having captured key towns to the north and south.
The army has threatened a "no mercy" tank assault on the TPLF leadership in Mekele, warning civilians to leave while they still can, raising concerns among rights activists.
"Treating a whole city as a military target would not only (be) unlawful, it could also be considered a form of collective punishment," Human Rights Watch researcher Laetitia Bader wrote on Twitter.
Abiy urged the people of Mekele to side with the national army against the TPLF, "in bringing this treasonous group to justice."
Hundreds of people are reported to have been killed in nearly three weeks of fighting which has seen warplanes bomb the region and tanks enter the fray.
Amnesty International also documented a gruesome massacre in which "scores and likely hundreds" of people were stabbed and hacked to death in the southwest town of Mai-Kadra.
Tens of thousands of Ethiopians have meanwhile fled west into Sudan and rockets have hit Eritrea to the north, spurring fears the internal conflict risks instability beyond its borders.