Ethiopian Prime Minister Abiy Ahmed vowed further airstrikes after jets bombed the northern Tigray region on Friday amid reports that Tigrayan forces had seized control of federal military sites and weapons.
The military conflict, which has raised fears of civil war, broke out on Wednesday following weeks of tension over Tigray's unilateral decision to elect a regional administration against Abiy's wishes.
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"Our operation aims to end the impunity that has prevailed for far too long and hold accountable individuals and groups under the laws of the land," Abiy said on Twitter on Saturday.
He spoke as parliament in the capital, Addis Ababa, approved the formation of an interim government for the region – a step aimed at denying the legitimacy of Tigray's regional government.
The escalating conflict drew international calls for restraint as political analysts and diplomats warned that a slide into civil war would not only destabilize the country of 110 million people, but hurt the broader Horn of Africa region.
Abiy, who won last year's Nobel Peace Prize, said he launched the airstrikes after the Tigray People's Liberation Front (TPLF) attacked a federal military base and tried to steal equipment. He said "the last red line" had been crossed.
Civilians in the northern region should avoid "collateral damage" by not gathering outside as strikes would continue, Abiy said in a televised speech late on Friday.
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Diplomats, regional security officers and aid workers have said fighting is spreading in northwestern areas along Tigray's border with the Amhara region, which is backing the federal government, and near the border with Sudan and Eritrea.
Sudan partially closed its border with Ethiopia due to the violence, state news agency SUNA reported on Saturday.
Abiy said on Friday that government troops had seized control of the town of Dansha, near the border area, from the TPLF.
His government cut phone and internet communications to the region, according to the digital rights group Access Now, making it impossible to verify official accounts. Government officials accused the TPLF of shutting down communications.
After toppling a Marxist dictator in 1991, the TPLF led the country's multi-ethnic ruling coalition until Abiy took office in 2018. For those decades, Tigrayans dominated the military.
Abiy, who is from the Oromo ethnic group, Ethiopia's largest, has sacked many senior generals as part of a crackdown on past rights abuses and corruption which 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 Ethiopia's army will split along ethnic lines, with Tigrayans defecting to the regional force. There are signs that is already happening, analysts said.
Tigrayan forces are 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 Ethiopia's four military commands 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 mobilizing 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, Amnesty International said.
Troop redeployments from near the border with Somalia will make that area "more vulnerable to possible incursions by Al Shabaab," the al Qaeda-linked insurgency trying to overthrow the government in Somalia, according to the UN report.