Heavy fighting broke out in Ethiopia's northern Tigray region on Wednesday, diplomatic sources said, after the prime minister launched military operations in response to what he said was an attack on federal troops.
Tensions have been escalating since September when Tigray held regional elections in defiance of the federal government, which called the vote "illegal". In recent days, both sides accused each other of plotting a military conflict.
Early on Wednesday, the local ruling party, the Tigray People's Liberation Front (TPLF), tried to steal artillery and other equipment from federal forces stationed there, Prime Minister Abiy Ahmed's office said.
"The last red line has been crossed with this morning's attacks and the federal government is therefore forced into a military confrontation," it said, adding that the aim was to prevent instability engulfing the country and region.
The prime minister's spokesman Billene Seyoum told Reuters later that military operations in Tigray had commenced, without elaborating. Two diplomatic sources in Addis Ababa said heavy fighting, including artillery fire, had broken out in the northern region, which borders Eritrea.
Tigray's local government said the Northern Command of the federal military, which is stationed in the region, had defected to its side, a statement which Billene described as "false information".
The prime minister's office said the federal government had declared a six-month state of emergency in Tigray to be overseen by the chief of staff of the armed forces.
Redwan Hussein, spokesman for a newly-established State of Emergency Task Force, said the government viewed the TPLF as the real enemy, not the Tigray region.
"This conflict is with a very small group, with narrow vested interests, which is hell-bent on destabilising the national order," Redwan told a news briefing.
He told Reuters the TPLF assault took place at the Northern Ethiopia Command's base near Mekele, and in Dansha, near Humera. Asked if negotiations were an option, he replied, "not yet". There was no immediate comment from the TPLF.
The US Embassy in Ethiopia urged both sides to de-escalate.
"We strongly encourage all parties to prioritize civilians' safety and security," it said in a statement.
The internet was shut down in the region, internet access monitor NetBlocks said, after earlier reports that authorities had shut down telephone and internet services.
Tigrayans dominated Ethiopian politics after guerrilla fighters ousted a Marxist dictator in 1991, but their influence has waned under Abiy. Last year, the TPLF quit his ruling coalition.
Since Abiy came to power in 2018, many senior Tigrayan officials have been detained, fired or sidelined, in what the federal government describes as a clamp-down on corruption but Tigrayans see as a means to quell dissent.
Tigray's population makes up 5% of Ethiopia's 109 million people, but it is wealthier and more influential than many other, larger regions and has a well-trained army.
Ethiopia has suffered multiple outbreaks of violence since Abiy took office. At the weekend, gunmen killed 32 people and torched more than 20 houses in western Ethiopia.