R. Kelly has been charged with 10 counts by the Cook County State's Attorney.

Prosecutors hit him with 10 counts of aggravated criminal sexual abuse Friday morning. TMZ has learned 9 of the 10 counts involve alleged victims ranging in age from 13 to 16 years old. One of them is the subject of 4 different counts. There are a total of 4 alleged victims.

Sources connected to Kelly tell TMZ the singer plans to voluntarily turn himself into authorities tonight. Still, prosecutors will reportedly appear before a judge today seeking an arrest warrant for him.

The criminal sexual abuse charge is a class 2 felony in Illinois, and each charge carries a max sentence of 3 to 7 years in prison.

A grand jury had convened about a week ago to investigate the alleged sex tape that Michael Avenatti handed over to authorities. TMZ broke the story ... 2 women testified for the grand jury over the last week, including one who provided physical evidence. We're told as many as a dozen women came forward to testify.

Sources connected to the case tell us the tape was a pivotal force leading to the charges. We're told that Avenatti and his client spent a significant amount of time with the Cook County State's Attorney and the grand jury in the last few weeks.

As we reported, Avenatti says he uncovered the VHS tape during a months-long investigation into allegations his clients made about Kelly having sex with minors. The tape reportedly shows Kelly having sex with a girl who seems to be 14 -- with both Kelly and the girl referring to her genitals and other body parts as being 14 years old.