"Crude lies and intimidation are backward steps that dishonor (Economic Community of West African States chief Umaro Sissoco Embalo) and at the same time tarnish ECOWAS' image," Colonel Amara Camara, a senior junta figure, told AFP.
At the end of July, Embalo said he had convinced Guinea's junta to hasten the return to democracy.
Three years in power before a return to civilian rule is "unacceptable for ECOWAS," Embalo, who is also president of Guinea-Bissau, said Wednesday.
"Unacceptable and non-negotiable," he added, in an interview with France's RFI and France 24 broadcasters, a day before an ECOWAS summit on the sidelines of the United Nations General Assembly in New York.
The poor but mineral-rich nation has been ruled by the military since a coup in September 2021 that ousted president Alpha Conde, in power since 2010.
Embalo said in the interview that if the junta maintained that timetable, there would be sanctions -- "heavy sanctions, even".
The West Africa bloc has been struggling with a string of military coups in the region in the past two years.