Fighting in Ethiopia's Tigray region has killed hundreds of people, threatening to destabilise Africa's second most populous nation.
Reuters reporters travelling in the northern area bordering Eritrea and Sudan, and the neighbouring Amhara region saw trucks packed with armed militia and pickups with machine-guns mounted on the back rushing to the front line in support of the federal government push.
The continent's youngest leader at 44, Ethiopia's Prime Minister Abiy Ahmed won the Nobel Peace Price last year for democratic reforms and for making peace with Eritrea.
But last week Mr Abiy, who comes from Ethiopia's largest ethnic group, the Oromo, launched a campaign against forces loyal to Tigrayan leaders whom he accused of attacking a military base in the town of Dansha.
On Monday, he sought to quash speculation that his nation was on a path to civil war, saying the idea is "unfounded and a result of not understanding our context deeply." He thanked Ethiopia's "friends" for "expressing their concern".
Mr Abiy has said jets have been bombing arms depots and other targets. Aid workers and security sources have reported heavy fighting on the ground.
A military official in Amhara, on the side of the federal troops, told Reuters that clashes with Tigrayan forces in Kirakir, near the Tigray-Amhara border, had killed nearly 500 Tigrayan forces.
Three security sources in Amhara working with the federal troops said the Ethiopian army had also lost hundreds in the original battle in Dansha.
The Tigray People's Liberation Front (TPLF), which governs the region, is battle-hardened from both the 1998-2000 war with Eritrea and the guerrilla war to topple Mengistu Haile Mariam in 1991. TPLF forces and militia allies number up to 250,000 men and possess significant hardware, experts say.
Tigrayans account for just 5 per cent of Ethiopians but had, before Mr Abiy's premiership, dominated politics since rebels from their ethnic group toppled Marxist military rule in 1991.
They say Mr Abiy's government has unfairly targeted them as part of a crackdown on past rights abuses and corruption.
"These fascists have demonstrated they will show no mercy in destroying Tigrayans by launching more than 10 air strike attempts in Tigrayan cities," the TPLF said via Facebook.
There was no immediate response from the prime minister's office, or from the spokesman of the state of emergency task force established by the government.
The army said it was intensifying attacks and that large numbers of Tigrayan special forces and militia were surrendering. It denied a TPLF claim of downing a jet.
Mr Abiy, a former soldier who fought alongside Tigrayans against Eritrea, has so far defied calls from the United Nations and others to negotiate.