Some of the rebel groups in the new alliance have previously fought against each other but they say they will now work together against their common enemy.
However analyst Edward Bach from advisory firm Verisk Maplecroft told the AFP news agency that the groups were “unlikely to share weapons… as your ally today can be your enemy tomorrow”.
Amhara’s Fano group fought alongside federal forces against the TPLF during the Tigray war.
It however turned against the federal government in an armed insurgency less than a year after the war ended, after refusing government orders to disarm.
Abdikadir Addaani Hirmooge, the spokesman for the Ogaden National Liberation Front (ONLF), which is part of the alliance, told the BBC that the groups in the new coalition were working to bring together communities that have been divided against one another.
“Our objective is for the communities to have democracy and to exercise their right to self-determination, to genuinely govern themselves,” he said.
He said that the government had not respected a peace deal signed in 2018 to end the conflict in the Somali region.
“Ethnic conflict, insecurity, and mutual oppression and pushing each other aside have not been eradicated, resulting in a need that has affected every ethnic group,” he said.
The government has been fighting the OLA since 2018.
The announcement of the Alliance for Survival coalition comes months after reports of an alleged alliance between TPLF and neighbouring Eritrea.
Abiy responded by saying he had faith in Ethiopia’s “defensive capabilities”.
“Even if others were added, we do not have an iota of fear regarding Ethiopia’s sovereignty,” he told lawmakers in July.
The country held a general election in June, with Abiy’s Prosperity Party retaining its overwhelming parliamentary majority, despite the poll being overshadowed by conflict, accusations of repression and little participation by opposition parties.
The Fano and OLA rebel groups rejected the election and its results.
The Tigray region and its six million inhabitants were completely excluded from the