The African Union (AU) said it suspended Niger on Tuesday after a coup by the West African state's military in late July.
The AU also reiterated calls for the coup leaders to release elected President Mohamed Bazoum and stand down.
It called on all member states to "reject this unconstitutional change of government and to refrain from any action likely to grant legitimacy to the illegal regime in Niger."
AU to assess implications of ECOWAS deployment
Over the weekend, coup leader Abdourahmane Tchiani said that transitioning power to civilian rule could take up to three years.
Tchiani's remarks came as a delegation from the Economic Community of West African States (ECOWAS) met with the junta leader on Saturday.
Nigeria's former military president, Abdulsalami Abubakar, who led the delegation said the talks were "very fruitful" and that he had hope the crisis could be solved through diplomacy.
ECOWAS diplomacy
ECOWAS said last week said it had agreed to an undisclosed "D-Day" for a possible military intervention if diplomatic efforts fail.
A top official for the West African regional bloc said that leaders gathered at a meeting last week had fine-tuned details of the military intervention.
The bloc has already imposed sanctions on Niger and approved the deployment of a "standby force to restore constitutional order" in Niamey.
On Tuesday, the AU's Peace and Security Council requested the AU Commission "to undertake an assessment of the economic, social and security implications of deploying a standby force in Niger and report back to Council."
Speaking at the weekend, Tchiani warned that a military intervention against the junta would not be easy.
