Tigray rebels in Ethiopia told AFP on Thursday they were in a state of "full-blown war" with the federal government, with reports of hundreds killed and heavy artillery attacks in neighbouring states.
Tensions have been rising for months between the federal government and the authorities in the northern Tigray state, who fought a devastating civil war in 2020-2022 that killed more than 600,000 people, according to African Union estimates.
The two sides accuse each other of triggering a return to open conflict with attacks this week, and there are fears the fighting could draw neighbouring Eritrea into a wider war.
The Tigray People's Liberation Front (TPLF) seized control of three local airports and launched attacks into the neighbouring states of Afar and Amhara on Wednesday.
A humanitarian source in Afar told AFP there were heavy artillery attacks by the rebels on Thursday as they attempted to take control of the town of Yallo, near the Tigrayan border.
"We are in the situation of full-blown war now," TPLF vice president Amanuel Assefa told AFP, confirming that Tigrayan forces were fighting alongside local armed groups in Afar and Amhara.
The federal army said it had killed 272 TPLF soldiers as they launched attacks in North Wollo Zone in Amhara. AFP could not independently verify the figures and no casualties were given for the federal army or civilians.
There was fighting around Lalibela, home to medieval rock churches, which are UNESCO World Heritage sites.
"Heavy weapons fire can be heard on the outskirts of Lalibela. The situation here is difficult," a priest in the town told AFP.
Analysts say the Tigrayans are repeating their strategy from the last war -- pushing south through Amhara towards the capital, Addis Ababa, while the offensive in Afar is likely aimed at cutting off supplies from Djibouti, which provides almost all of Ethiopia's international trade cargo, including fuel.
"Their stated aim is to take Addis, but (the) tactical manoeuvres to reach the city are not yet known," said regional expert Kjetil Tronvoll, of Oslo New University College.
Back in Tigray, prices for basic goods spiked as locals flocked to stock up on supplies, fearing a repeat of a blockade imposed during the last war.
"There is panic in the community," said Samuel Gebreslassie, 37, who works in a spice shop in the Tigray capital, Mekelle. "There is deep fear that banks, telecom networks, electricity and basic goods could be cut off again."
Ethiopian President Taye Atske Selassie Amde, speaking at the UN General Assembly on Wednesday, decried "the forces of destruction and mayhem" and "interference in our internal affairs by adversarial elements".
Analysts say the Tigray rebels have support from Eritrea, which fears landlocked Ethiopia is planning to invade it to gain access to the Red Sea.
The TPLF's Assefa told AFP "we have no information about Eritrea's plan". Asked if they would request Eritrean intervention, he said: "Not yet."
The Sudanese army is also angry with Ethiopia over its alleged support for its paramilitary enemies, the Rapid Support Forces -- threatening to further complicate the situation.
The renewed fighting comes at an awkward moment for the United States, which only this month lifted sanctions on Ethiopia and Eritrea related to the last civil war, saying the "national emergency... has expired".
The US embassy sided with Ethiopia's government on Wednesday, saying it was "disappointed to see the leadership of the TPLF... launch a large-scale offensive".
The TPLF forged an anti-government alliance last weekend with the Fano in Amhara and five other armed groups around the country.
The dynamics have changed since the last civil war, when the Fano and Eritrea both fought with the government against the Tigrayans, only to be frustrated when a peace deal was signed in 2022.
The Pretoria Peace Agreement of 2022 maintained an uneasy calm until late last year, when clashes resumed.
The federal government has since launched drone strikes in Tigray and massed troops at the regional border.
The TPLF ruled the whole of Ethiopia from 1991 to 2018 before being sidelined with the rise of Prime Minister Abiy Ahmed, eventually triggering the civil war.
Rights groups have accused the TPLF of a campaign of forced recruitment this year as it prepared for renewed conflict, even as around one million people remained displaced from the last war.