R. Kelly, Allegations He Targeted Underage Girls for 'Slavery'

R. Kelly turned underage women into slaves ... so claims the family of one of the young women who is living with the rapper.

Joycelyn Savage's father, Timothy, tells us Kelly started some of these relationships when the girl was 17, and in his book that's a crime. Timothy goes on to claim the singer's relationship with these women turned physically abusive.

But Timothy isn't done with his accusations. He compares the "relationships" to slavery, saying there was no free will on the part of the young women.

Timothy also vehemently denies Joycelyn's allegations he set her up with R. Kelly ... even suggesting the singer forced her to say that.

He also insists the FBI is in the throes of an investigation, especially targeting Florida.