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 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 enormous protests against ex-President Ibrahim Boubacar Keïta only threatens further instability.
What happened to the former president?
The ousted former president left the country last week.
The 75-year-old former leader flew to the United Arab Emirates (UAE) on 5 September for medical treatment, after suffering a minor stroke, military officials said.
His former chief of staff said he could be away for up to 15 days.
After the coup, West African leaders said they wanted a rapid return to civilian rule. Mali's new military rulers had previously said they wanted the interim period to last for two years.
"We make a commitment before you to spare no effort in the implementation of all these resolutions in the exclusive interest of the Malian people," Col Assimi Goita, the head of Mali's military junta, said.
President Keïta was overthrown on 18 August following mass protests against his rule over corruption, the mismanagement of the economy and a dispute over legislative elections.
The coup sparked international condemnation, but it was welcomed by many Malians.
Mr Keïta was detained by the military, but later freed.
This was the fourth coup in the West African state since it gained independence from France in 1960.
A previous coup in 2012 led to militant Islamists exploiting the instability to seize territory in northern Mali. French troops helped regain territory, but attacks continue.
The coup leaders earlier promised to respect international agreements on fighting jihadists.
Thousands of French, African and UN troops are based in the country to tackle the militants.