The attackers are said to have driven into the camps on motorcycles.
"They didn't talk to anyone. They just started killing. I saw dozens of corpses," a source from the area told AFP.
Several people the news agency spoke to said the death toll was closer to, or even higher than, 50.
It has not been confirmed who was behind the attacks, but sources told AFP they believed the terrorist group IS was responsible.
Civil war has been ongoing on several fronts in Mali for some time. The internal fighting began in January 2012 in connection with an uprising by the Tuareg ethnic group in the north of the country. Large parts of Mali have since been plunged into deep and brutal misery.