The opposition coalition which led mass protests in Mali ahead of last month's coup has rejected a transition charter 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.
The M5-RFP group said the document was an attempt by military leaders to "grab and confiscate power"
"It concerns in particular the profile of the president of the transition who must be a civilian and non-military personality, since this would subject us to the sanctions of the international community, hence ECOWAS, and the terms and conditions for the appointment of this president. And we have heard that it would be by a panel whereas this aspect was never debated in the plenary." Ibrahim Ikassa Maïga, one of the leaders of the June 5 Movement explained.
A meeting is planned on Tuesday in Accra between ECOWAS and Mali.
Regional powers worried that political instability will undermine a years-long fight against armed groups across West Africa, have pushed for a swift transition back to civilian rule.
ECOWAS has warned the military government must designate a civilian leader to head a one-year transition period by September 15 or else the country could face further sanctions.