Ethiopian jets bombed the Tigray region on Friday and Prime Minister Abiy Ahmed pledged more air strikes in the escalating conflict, as reports emerged that Tigrayan forces had seized control of key federal military sites and weapons.
Civilians in the northern region should avoid "collateral damage" by not gathering outside as strikes would continue, Mr Abiy said on Friday evening in a televised speech, defying international pleas to both sides for restraint.
The developments signalled how fast the days-old conflict was hurtling towards civil war that experts and diplomats warn would destabilise the country of 110 million people and hurt the broader Horn of Africa.
A simmering row between Mr Abiy's federal government and his former Tigrayan allies exploded on Wednesday after Mr Abiy ordered a military campaign. Mr Abiy, who won last year's Nobel Peace Prize, accused the Tigray People's Liberation Front of attacking a federal military base and trying to steal equipment. He said "the last red line" had been crossed.
The government then cut phone and internet communications to the region, according to the digital rights group Access Now, making it impossible to verify official accounts. The government accused the TPLF of shutting down communications.
Diplomats, regional security officers and aid workers have told Reuters that fighting is spreading in the northwestern part of the country, along Tigray's border with the Amhara region, which is backing the federal government, and near the border with Sudan and Eritrea.
Mr Abiy said on Friday that government troops had seized control of the town of Dansha, near the border area, from the TPLF.
After toppling a Marxist dictator in 1991, the TPLF led the country's multi-ethnic ruling coalition until Mr Abiy took office in 2018. For those decades, Tigrayans dominated the military. Mr Abiy has sacked many senior generals as part of a crackdown on past rights abuses and corruption that Tigrayans complain unfairly targets them.
Tigrayan forces are battle-hardened and possess significant stocks of military hardware, experts say. Their regional troops and associated militias number up to 250,000 men, according to the International Crisis Group think tank.
One of the biggest risks is that the Ethiopian army will splinter along ethnic lines, with Tigrayans defecting to the regional force. There are indications that is already happening, experts said.
Tigrayan forces were in control of the federal military's Northern Command headquarters in the city of Mekelle, according to a United Nations internal security report dated Friday and seen by Reuters.
The Northern Command is one of the four military commands of the country and controls the border with Sudan, Djibouti and Eritrea.
Tigrayan forces have seized "heavy weapons" from several of the command's depots, the report read. It said that the command is the most heavily armed and contains "most of the military’s heavy weapons including the majority of the country’s mechanised and armoured units, artillery and air assets."
The government is mobilising troops from around the country and sending them to Tigray, risking a security vacuum in other parts of the country where ethnic violence is raging. More than 50 people were killed by gunmen from a rival ethnic group in western Ethiopia on Sunday, according to Amnesty international.
Troop redeployments from near the border with Somalia will make that area "more vulnerable to possible incursions by Al Shabab," the Al Qaeda-linked insurgency trying to overthrow the government in Somalia, the UN report read.