Regional bloc the Economic Community of West African States (ECOWAS) had pressured the military who seized power in a 2021 coup to organize elections before the end of 2024.
But the West African nation's prime minister in mid-March suggested the generals would have to delay a return to civilian rule until at least 2025.
The Forces Vives de Guinee "strongly condemn the Guinean junta's decision not to hold presidential elections in December 2024, in accordance with the agreement reached with ECOWAS in October 2022," the collective said in a statement.
"After more than two years of transition, Guinea still has no draft constitution, no electoral code, no election management body and no (electoral) register," it added.
The group accused the junta of restricting public freedoms and harassing political leaders.
It called for the "restoration of public freedoms and (a) return to constitutional order before December 31," adding that it would no longer recognize the military in power after this deadline.
"The postponement of the end of the transition without any consultation with the socio-political players compromises any serious dialogue with the junta," the statement said.
It called for an independent and consensual electoral management body to be set up, the 2010 constitution to be reviewed and submitted to a referendum, with the electoral code to be revised.