Rebel fighters in the Tigray region of Ethiopia are continuing to gain ground after recapturing the regional capital Mekelle from government forces.
The rebels have now entered the town of Shire, about 140km (90 miles) to the north-west, according to UN officials.
Eritrean troops backing the Ethiopian army had earlier abandoned the city.
The government has declared a ceasefire in the eight-month conflict, but the rebels have vowed to drive their "enemies" from Tigray.
The fighting between the Tigray People's Liberation Front (TPLF) and government forces has left thousands of people dead.
More than two million have been displaced and 350,000 pushed towards famine.
The fighting began in November, when rebels rejected political reforms and captured army bases. Government forces captured Mekelle later that month.
There were scenes of jubilation in the streets of the capital on Tuesday, a day after the rebels retook the city following a rapid offensive. The central government has called a "humanitarian ceasefire" in the region.
Rebel spokesman Getachew Reda told Reuters news agency that Tigrayan fighters would "destroy the enemy" by entering Eritrea and the Ethiopian region of Amhara - whose militias have also supported government forces.
"We have to ensure that the enemy... doesn't have the capability to threaten the security of our people anymore," he said.
The status of Eritrean troops remains unclear, although one resident in Shire told Reuters the Eritreans appeared to be moving north, towards the border.
The rebels are now in control of most of the region, the research organisation International Crisis Group said.
It is difficult to verify information in Tigray as communications have been cut.
A turning point?
Vivienne Nunis, BBC News, Nairobi
With rebels seizing back control of Mekelle, Prime Minister Abiy Ahmed appears to have had few options left when he unilaterally declared a ceasefire.
But by framing the decision as a "humanitarian" one, the government in Addis Ababa is attempting to save face.
So what now? The rebels have so far ignored the ceasefire saying they are intent on driving out all so-called "invading enemies".
The international community will be watching to see whether the ceasefire is a turning point, and in particular, whether humanitarian groups can now travel freely in the region to deliver supplies to the millions of people in desperate need of food.
Tigray - the basics
- Ethiopia is divided into 10 regional states defined on ethnic grounds and described as largely autonomous, but with central institutions
- In 2018, following anti-government protests, Abiy Ahmed took over as PM and introduced reforms
- Powerful politicians from Tigray, Ethiopia's northernmost state, accused Mr Abiy of trying to increase federal power
- Relations worsened and, after the government accused Tigrayan rebels of attacking military bases, the Ethiopian army moved in in November
- Mr Abiy declared the conflict over in late November, but fighting continued and increased ahead of national elections on 21 June
All sides in the conflict have been accused of mass killings and human rights violations.
On Tuesday, senior US state department official Robert Godec said Washington would not stand by in the face of the "horrifying atrocities" being committed in Tigray.
State department spokesperson Ned Price said the truce declaration could be positive if it led to steps to "end the conflict, stop the atrocities, and allow unhindered humanitarian assistance".
The UN has said there was a situation of famine in northern Ethiopia - a claim Ethiopia's government denies.