For months, the singer R. Kelly has faced federal charges that he sexually exploited underage girls and young women, but on Friday prosecutors added a lurid wrinkle: They accused him of knowingly exposing two people to a venereal disease.

An updated indictment said Mr. Kelly knew he had herpes and yet had unprotected sex with a woman and an underage girl without telling them.

The woman, identified only as Jane Doe No. 6, ended her relationship with Mr. Kelly in 2018 after learning she had contracted an “infectious venereal disease” from him, according to an earlier government filing. They met in 2017, when she was 19 years old, after Mr. Kelly performed at a concert, the filing said.

In its new filing on Friday, the government not only identified the disease as herpes but also added criminal charges associated with knowingly spreading it.