- The army chief General Seare Mekonnen and a retired general were also killed on Saturday evening in what appeared to be a co-ordinated attack.
Ethiopia's army chief was shot dead by his bodyguard just hours after an attempted coup in Amhara state left the regional president and another top adviser dead, a spokeswoman for the prime minister said Sunday.
The spokeswoman Billene Seyoum told journalists a "hit squad" led by Amhara's security chief Asaminew Tsige burst into a meeting on Saturday afternoon, injuring regional president Ambachew Mekonnen and another top official who both died of their wounds.
Later that evening in what appeared a "co-ordinated attack", army chief Seare Mekonnen, and a retired general who was visiting him, were killed by his bodyguard, said Billene.
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.
The US state department has warned its staff in Addis Ababa to stay inside, saying it is aware of reports of gunfire in the city on Saturday.
Information is scanty, with reports that the internet has been down, but Prime Minister Abiy, dressed in military fatigues, went on TV to make his announcement.
He said the chief of staff had been shot by "mercenaries".
The Amhara regional officials were killed by their own colleagues during a meeting, he added.