Ethiopia's government and the party in control of the northern region of Tigray have accused each other of launching offensives, escalating fears of a return to full-scale conflict.
Getachew Reda, a cabinet minister and adviser to Ethiopia's prime minister, said Tigrayan fighters had taken control of federally administered airports in Tigray and launched offensives in neighbouring Afar and Amhara regions.
Earlier, the Tigrayan authorities said their forces had been forced to enter a "defensive war". The statement followed reports of drone strikes in Tigray.
The two-year war in Tigray ended in 2022 - but over recent months both sides have been accusing each other of violating a peace deal.
It was one of the most deadly conflicts this century - the African Union's mediator estimated some 600,000 people died as the fighting drove the region to the precipice of famine.
On Sunday, the Tigray People's Liberation Front (TPLF), the party that runs Tigray, announced an alliance with six other armed groups in Ethiopia to remove the government in Addis Ababa.
"It is rather heartbreaking to learn that, despite efforts by many, including the international community, to avoid yet another round of war in Tigray, the TPLF leadership early this morning launched an all-out offensive against government positions in Afar and Amhara," Getachew said in a statement shared on social media.
The adviser to Prime Minster Abiy Ahmed previously led Tigray's interim administration, but he fell out with the TPLF in 2025 and joined the federal government.
Following the seizure of the airports, Ethiopian Airlines has cancelled all flights to Tigray.
Residents of Tigray's main city of Mekelle told the BBC that local forces had taken over control of the city's airport from the national police early on Wednesday.
This followed reports of drone strikes in Tigray in recent days.
On Tuesday, a strike in the southern town of Alamata killed at least 14 people and injured 22 others, according to the Tigrayan authorities.
The town's mayor, Mogos Shiferaw, told the BBC that more than five drones and one fighter jet had carried out more than 21 strikes starting at around 03:30.
"This caused a lot of psychological trauma in our city and our people were in a state of panic," he said.
Mogos said all those killed and injured were civilians, accusing federal forces of targeting two secondary schools.
He believed they were struck on suspicion that they were being used by Tigrayan forces.
But the mayor said the schools, which had served as federal military bases during the civil war, were unoccupied as the academic year had not yet begun.
The BBC has not independently verified the allegations and the government has not commented on the alleged strikes.
On Wednesday, the Tigray authorities accused Addis Ababa of launching an "open invasion" of the region, urging people to support the regional forces and maintain unity.
It further accused the government of violating international humanitarian and human rights laws, saying public services and critical infrastructure had been disrupted.
Meanwhile, the US State Department's Bureau of African Affairs has condemned a separate drone strike that it said took place on Monday, targeting a convoy of Catholic vehicles carrying food aid.
It called for an investigation and urged all parties to resolve their differences through dialogue and take steps to prevent similar incidents.
Both Addis Ababa and TPLF leaders have faced criticism over delays in implementing key provisions of the Pretoria Agreement, the AU-brokered deal that formally ended the conflict in November 2022.
In July, Prime Minister Abiy accused the TPLF of preparing for renewed conflict during an address to parliament.
Just before the general election in May, the TPLF restored its pre-war administration, disbanding an interim one appointed by Abiy.
There have also been reports that the TPLF has forcibly recruiting young men to join its forces.
