Ethiopian Prime Minister Abiy Ahmed sought to re-establish authority over the northern Tigray region on Saturday, a day after launching air strikes amid reports that Tigrayan forces had seized control of federal military sites and weapons. The military conflict, which has raised fears of civil war in a nation plagued by ethnic violence, broke out on Wednesday following weeks of tension over Tigray’s decision to defy Abiy by electing a regional government against his wishes. “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 self-declared regional administration. In Tigray, the regional government said a number of Tigrayans serving in the federal police and army had been sacked while others were put under house arrest, according to a Facebook post by its communications office. Tigrayans have dominated Ethiopia’s military and political life for nearly three decades. After toppling a Marxist dictator in 1991, the Tigray People’s Liberation Front (TPLF) led the country’s multi-ethnic ruling coalition until Abiy took office in 2018. Abiy, who won last year’s Nobel Peace Prize, said he launched the air strikes after the TPLF attacked a federal military base and tried to steal equipment. Urging civilians to stay indoors to avoid “collateral damage”, Abiy said in a speech late on Friday that air strikes would continue. The escalating conflict drew international calls for restraint as political analysts and diplomats warned that a slide into civil war would not only destabilise the country of 110 million people, but hurt the broader Horn of Africa region. Diplomats, regional security officers and aid workers said fighting was 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 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. BATTLE-HARDENED 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 and have seized “heavy weapons” from several of its depots, 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. As Abiy’s government mobilises troops to send to Tigray, other parts of the country roiled by ethnic violence could face a security vacuum, the U.N. report said. 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 U.N. report.