Musician R. Kelly. Picture: Ashlee Rezin/Chicago Sun-Times via AP

R. Kelly is being accused of sexual abuse by another woman.

The "Ignition" hitmaker is already facing 10 counts of aggravated criminal sexual abuse from four women, three of whom claim they were underage at the time of the alleged incidents, but he's now been accused of abuse by a fifth woman who also claims to have witnessed him performing sex acts with the underage women.

According to The Blast, the woman claims she was sexually abused by Kelly, and although she was adult herself at the time, she alleges to have seen him sexually abuse underage females during her time in an "extended relationship" with the singer.

The publication reports the unnamed woman - who wishes to remain anonymous - has spoken with federal investigators about her allegations, who will decide whether to pursue a federal indictment against the star.

The new accusations come after police in Detroit revealed Kelly - who was accused by several women of sexual abuse in the recently aired documentary series 'Surviving R. Kelly' - is under investigation over another allegation of underage sex, from a woman who claims he slept with her in 2001 when she was just 13.

Detroit Police Chief James Craig said: "We've received information from Chicago Police Department of a victim who made allegation of a criminal sexual conduct incident against R. Kelly. The incident allegedly occurred in the city of Detroit when the victim was 13 years old.

"Based on the information received, we have made several attempts to follow up with her. We have reached out, at the direction of the victim, to her lawyer, and we are eagerly waiting to speak to her.

"We, the Detroit Police Department, take criminal sexual assaults very seriously, as well as all acts of violence committed against our residents, and will investigate all cases equally and with vigor in efforts to bring justice to the victims and their families."

Kelly was previously arrested when he was charged with 10 counts of aggravated criminal sexual abuse, and was forced to post $1 million as bail for his freedom.

He has denied all allegations against him, and recently hit out at his critics, whom he accused of "trying to kill" him.

He ranted in an interview this week: "Quit playing, I didn't do this stuff. 

"This is not me. I'm fighting for my f*****g life! Y'all killing me with this s**t! I've given you 30 years of my f****g career! 30 years of my career! Y'all trying to kill me! You're killing me man!

"This is not about music! I'm trying to have a relationship with my kids and I can't do it! Y'all just don't want to believe the truth. Y'all don't want to believe it. This is not true! It doesn't even make sense! Why would I hold all these women! Their mothers and fathers told me, 'We're going to destroy your career.'"