Tigray rebels accused the African Union (AU) on Sunday of "bias" following the appointment by the pan-African organization of a mediator in the conflict that has been tearing northern Ethiopia apart for nearly a year.
"It would be naive to think that this mission could work," said on Twitter the spokesman for the rebels Getachew Reda, three days after the appointment of former Nigerian President Olusegun Obasanjo as representative of the AU in the Horn of Africa with the mission to "promote peace, security, stability, and political dialogue".
"Resolving a crisis requires at least the recognition of the existence, if not the importance, of a problem," he wrote.
"We find it difficult to understand how one can expect a constructive role from an organization that has given full meaning to the word partiality," he concluded.
Ethiopian Prime Minister Abiy Ahmed, for his part, has repeatedly rejected any proposal to hold talks with the group.
Addis Ababa has designated the TPLF a terrorist organization.
In late June, government forces withdrew from the Tigray regional capital of Mekelle after Addis Ababa announced a ceasefire.
The rebels rejected the offer and attacked the neighboring Amhara and Afar regions in their bid to march on the capital.
They have been accused of committing war crimes in the process.
Abiy shuttles to Entebbe, Kigali
The conflict has been a sensitive issue for the African Union, and Ethiopia's allies have prevented any discussion of the issue at the UN Security Council.
The conflict which was sparked last November by an attack on a federal army base by TPLF forces has threatened to further destabilize Africa's second-most populous country.
On Sunday, Abiy met with the leaders of Uganda and Rwanda in Entebbe and Kigali respectively.
According to the UN, the conflict has already left some 400,000 people in a near-famine situation.