An AFP journalist saw one body at the scene of the shootout -- the group's headquarters in the town of Xolapa, Guerrero state -- and another seven lying in wake in the homes of relatives.
A state government official said the death toll could rise to 16. The clash did not appear linked to today's congressional, gubernatorial and municipal elections.
The state government said in a statement that the clash involved rival factions of the United Front for Security and Development in Guerrero State (FUSDEG).
Self-defense forces are legal in Guerrero's indigenous communities, where they are allowed to apply their customs for law and order.