Ethiopian army chiefs, intelligence chief and foreign minister were sacked as fighting continued in the region north of Tigray.
Prime Minister Abiy Ahmed̵7;s office announced their replacement on Twitter – no reason has been given for the changes.
Long-standing tensions between the central and local governments in Tigray flared into clashes last Wednesday.
Dozens of casualties have been reported with more airstrikes reported.
There are concerns that conflict can lead to civil war, which can also destabilize neighboring countries.
The UN says there have been clashes between the federal army and the Tigrayan forces at eight different locations.
It states that nine million people are at high risk of being displaced by fighting. Aid was unable to reach Tigray because it was blocked – and contact with the area was cut off.
Who was reformed?
Commander in Chief: General Adem Mohammed is replaced by his deputy Gen Berhanu Jula
Chief of intelligence: Amhara state chief Temesgen Tiruneh Take over from Demelash Gebremichael, who becomes a police commissioner
Foreign Minister: Demeke Mekonen, who is deputy prime minister, also assumed the role of foreign minister from Gedu Andargachew.
The changes come a day after parliament, in an emergency session, voted to dissolve the Tigray government, saying it had “violated the constitution and endangered the constitutional system”.
Debretsion Gebremichael, the sacked Tigray leader, has now called on the African Union to intervene to prevent the country from falling into a spiral of civil war.
In a statement on television, he said Tigray would continue in self-defense until the federal government agrees to negotiate.
Last Wednesday, Mr Abiy ordered a military attack, after a military base in Mekelle was taken over by forces loyal to the Tigray government.
The Cabinet has also declared a state of emergency in the northern region bordering Eritrea, for six months.
What is behind the stress?
Tigray’s leaders dominated Ethiopia for years until Mr Abiy took power in 2018 due to anti-government protests and curbing their influence.
They say they have been unfairly targeted by purges and allegations of corruption, and say that Mr. Abiy is an illegal leader, as his duties have expired when he postponed the election due to coronavirus virus
Elections boiled in September after Tigray’s ruling party, the Tigray People’s Liberation Front (TPLF), defied a nationwide electoral ban and held a vote declared by the central government is illegal.
Things started to deteriorate last year after Mr Abiy dissolved the ruling coalition, which included a number of ethnic-based regional parties, and unified them into a single national party, the Prosperity Party, of which the TPLF refuse to participate.
On Sunday, Mr. Abiy, who won the 2019 Nobel Peace Prize for helping end a lasting conflict with Eritrea, urged other Ethiopians in a Twitter post about discrimination against the Tigray people, accounting for 6% of the population of more than 100 million people.