A pet monkey reportedly assaulted a schoolgirl, leading her family to seek revenge. Three men were killed along with the animal in initial clashes.
Days of fighting followed between the Awlad Suleiman and Guedadfa clans.
Casualties may be greater as the death toll is reportedly for the Awlad Suleiman group only.
Reports also suggest tanks, rockets, mortars and other heavy weapons were used in the fighting, in which at least 50 people were also wounded.
The three men reported as having the monkey at the time of the assault were from the Guedadfa community, the same as the late Libyan leader, Muammar Gaddafi.
Some reports say the monkey may have pulled off the girl's headscarf as well as scratching and biting her.
The relationship between the two communities is said to have been strained for many years.
Sabha is a hub for trafficking in migrants and arms in Libya's often neglected south.
Libya has been wracked by conflict since Col Gaddafi was ousted in 2011.