Sudanese opposition groups under the Declaration of Principles have boycotted internationally mediated peace talks and rejected an invitation to consultative meetings in Addis Ababa.
The coalition accused mediators of ignoring key conditions needed for lasting peace.
The five-party mechanism includes the United Nations, African Union, IGAD, League of Arab States and the European Union.
The alliance said a nationwide ceasefire must come before any political process and insisted any roadmap must be Sudanese-led without foreign interference.
It warned that rushed negotiations would only prolong the conflict.
Meanwhile, Democratic Alliance for Social Justice leader Mubarak Ardol confirmed his delegation will attend the Ethiopia meetings.
Ardol said political dialogue should eventually take place inside Sudan once conditions improve.
