Abdel-Fatau Musah, ECOWAS commissioner for political affairs, peace, and security, said on Friday that the Economic Community of West African States will not divulge to the coup plotters when and where it will strike.
He said the decision to intervene in the country has to be made by the heads of ECOWAS states.
ECOWAS has imposed sanctions on Niger and threatened the use of force if the coup leaders do not restore power to the ousted President Mohamed Bazoum by Sunday.
"All the elements that will go into any eventual intervention have been worked out here, including the resources needed, the how and when we are going deploy the force," Musah said at the close of a three-day meeting in Nigeria's capital Abuja.
The 15-member body sent a delegation to Niger on Thursday seeking an "amicable resolution," but a source in the entourage said a meeting at the airport with the junta's representatives yielded no breakthrough.
The block has said military intervention in junta-ruled Niger will be "the last resort.”
"We want diplomacy to work, and we want this message clearly transmitted to them that we are giving them every opportunity to reverse what they have done," Musah said.
Abdourahamane Tiani, the former leader of Niger's presidential guard and the leader of the military government, has vowed not to back down in the face of sanctions and threats.
Tiani has won the support of the military in Mali and Burkina Faso, citing ongoing insecurity as his main justification for taking power.
On Thursday, the military junta announced that any aggression or attempted aggression by ECOWAS would be met with an immediate and unannounced response by Niger's armed forces.
Mali and Burkina Faso have said they would treat an intervention in Niger as a "declaration of war" against them too and would come to Niamey's defense.
MNA/Press TV