The chief of staff of the Ethiopian army, Gen Seare Mekonnen, has been shot dead by his own bodyguard in the capital, Addis Ababa.
He and another officer died trying to prevent a coup attempt against the administration in Ethiopia’s northern Amhara region, PM Abiy Ahmed said.
In Amhara itself, regional governor Ambachew Mekonnen was killed along with an adviser.
The government says the situation is under control after arrests were made.
The prime minister has gone on TV to urge Ethiopians to unite in the face of “evil” forces set on dividing the country.
The US state department has warned its staff in Addis Ababa to stay inside.
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Ethnic violence has hit Amhara and other parts of Ethiopia in recent years.
Since his election last year, Mr Abiy has moved to end political repression by releasing political prisoners, removing bans on political parties and prosecuting officials accused of human rights abuses.
Africa’s oldest independent country, Ethiopia is also the continent’s second most populous (after Nigeria), with 102.5 million inhabitants from more than 80 different ethnic groups.
A transfer hub for long-haul air travel, it has one of the fastest-growing economies in the world, but a vast number of young Ethiopians are without work.