Commissioner for Political Affairs, Peace and Security Abdel-Fatau Musah said the "valiant forces of West Africa... are ready to answer to the call of duty".
That was as he addressed army generals from member states who were meeting in Ghana.
"By all means available, constitutional order will be restored in the country and this meeting today bears testimony to that."
Military officers in Niger deposed President Mohamed Bazoum on July 26.
They have defied calls from the United Nations, ECOWAS and Western powers to reinstate him.
That prompted West African heads of state to order a standby force to be assembled.
Musah listed past ECOWAS deployments in Gambia, Liberia and elsewhere as examples of readiness.
He also accused the junta of "playing cat-and-mouse" with the bloc.
"They are pretending, you know, that, oh now, they are ready for talks, but even as they are telling us they are ready for talks, they are seeking reasons, reasons to, uh, justify an unjustifiable coup d'etat."
Musah also strongly criticized the junta's announcement that it planned to put Bazoum on trial for treason.
The United Nations, European Union and ECOWAS have all expressed concerns over the conditions of his detention.
The junta has said it is open to talks to resolve the crisis.
In Niger's capital Niamey, large crowds have taken part in protests against ECOWAS and in favor of the coup leaders.
Demonstrators accuse ECOWAS of being manipulated by foreign powers and say they reject outside intervention.
