Ethiopia's army commander on Sunday accused Eritrea and Sudan of backing armed groups fighting its troops in the north of the country.
Heavy clashes have resumed between the Tigray People's Liberation Front (TPLF) and the federal government since Wednesday, raising fears of a return to a 2020-2022 civil war in which an estimated 600,000 people died.
The TPLF was now advancing towards the town of Afdeera, some 100 kilometres (60 miles) to the east.
The source estimated that at least 150,000 people have been displaced in Afar, but said it was impossible to give precise numbers.
Speaking on the army's YouTube channel, army chief Field Marshal Birhanu Jula said: "We are fighting forces that are organised and allied to serve the interests of external forces.
TV station attack
The TPLF has allied with seven armed groups around the country, and appears to repeating a strategy from the last war of pushing south through Amhara towards Addis Ababa.
The headquarters of Tigrai TV, seen as the key outlet for the rebel authorities in the Tigrayan capital, Mekelle, was hit by a drone on Sunday.
"We heard a loud bang from a drone strike elsewhere and we fled the building," a journalist from the station told AFP, speaking on condition of anonymity.
The channel has not commented on the incident.
Read moreTigray TV station hit by drone, rebels advance in north Ethiopia
Another journalist said the station, which has around 400 employees, was off-air after the attack. No reports of casualties were immediately available.
The federal government in Addis Ababa said on September 21 that Tigrai TV had been suspended "indefinitely", and banned other outlets from broadcasting its reports.
Read moreTigray rebels seize airports
Blockade
Communications have been limited since Friday when telecoms providers reported major disruption to phone and internet services in Tigray, making reporting on the conflict difficult.
Many in Tigray fear a repeat of a blockade imposed by the federal government during the 2020-2022 conflict when electricity, banking, and almost all aid were cut off.
United Nations chief Antonio Guterres raised the alarm on Friday, his spokesman saying Guterres was "particularly troubled by reports of the use of drones as well as incidents of harm to civilians".
The government has a significant military advantage, with a large arsenal of drones, some 500,000 troops, and support from abroad, notably the United Arab Emirates.
But the conflict could draw in neighbouring Eritrea on the side of the rebels, as it fears landlocked Ethiopia has been planning to invade and seize a direct point of access to the Red Sea.
The TPLF ruled all of Ethiopia from 1991 to 2018 before being sidelined with Abiy's rise to the prime minister's post.
That triggered a civil war marked by widespread war crimes and sexual violence.
The Pretoria Peace Agreement of 2022, brokered by African institutions and Washington, maintained an uneasy calm until last year. But it was never fully implemented, leaving around one million people unable to return to their homes.
Sporadic clashes then resumed, with the federal forces launching multiple drone strikes in Tigray in recent months and massing troops at the border.
Rights groups have accused the TPLF of a campaign of forced recruitment this year as it prepared for renewed conflict.
(FRANCE 24 with AFP)
