The opposition coalition which led mass protests in Mali ahead of last month's coup has rejected a transition charter.
On Saturday, the country's military leadership agreed to establish an 18-month interim government until an election could take place.
It followed three days of talks with the opposition and civil society groups. But the M5-RFP group, which took part in the negotiations, said the resulting document was an attempt by military leaders to "grab and confiscate power".
It also said the document did not take into account what it said was a majority vote for a civilian interim leader, and "did not reflect the views and decisions of the Malian people".
West Africa's regional bloc, Ecowas, had also called for the interim president to be a civilian, but the military leadership says a civilian or a soldier can fill the role.
The interim charter announced by the military leaders also states that an interim legislative body is to be established comprising M5-RFP members.
Mali is struggling with intense Islamist and ethnic violence, as well as a faltering economy.
The BBC's Africa Editor Mary Harper says the deep tensions between the military and the group which led to enormous protests against ex-President Ibrahim Boubacar Keïta only threatens further instability.
