CHICAGO (CBS) — R. Kelly pleaded not guilty Thursday to new sexual assault charges filed by Cook County prosecutors last week, the most serious criminal charges filed against the embattled R&B singer to date.

Last week, a new grand jury indictment charged Kelly with 11 new counts, including aggravated criminal sexual assault, criminal sexual assault and aggravated criminal sexual abuse. The four aggravated criminal sex assault charges are class X felonies and carry prison terms of up to 30 years if he’s convicted.

“A Class X felony is the most serious class of felony in Illinois, other than murder, based on the penalty for it of 6 to 30 years. So clearly the prosecutor is trying to get an enhanced sentence here. Whether they can prove it certainly remains to be seen,” former Cook County prosecutor Steven Block said.

At a brief arraignment hearing Thursday morning, Kelly pleaded not guilty to the new charges. Prosecutors did not seek any changes in his bond, so Kelly will remain free on bail pending trial.

His next hearing on the new case and the previous charges has been scheduled for June 26.

The new charges follow earlier allegations the singer sexually assaulted four women, three of them when they were minors. These latest charges in the case center on one of those victims, identified as JP.

According to the indictment, R. Kelly engaged in sex acts with JP in January 2010 “by the use of force or threat of force and … acted in such a manner as to threaten or endanger the life of JP.”

Kelly already has pleaded not guilty to the earlier charges.

Prosecutors have identified the victims only by initials, and the dates of the alleged abuse:

• H.W. (13-16 years of age), victim of four counts of aggravated criminal sexual abuse between May 26, 1998, and May 25, 1999;
• J.P. (13-16 years of age), victim of three counts of aggravated criminal sexual abuse between May 1, 2009, and Jan. 31, 2010;
• R.L. (13-16 years of age), victim of two counts of aggravated criminal sexual abuse between Sept. 26, 1998, and Sept. 25, 2001;
• L.C. (no age given), victim of one count of aggravated criminal sexual abuse on Feb. 18, 2003.

Greenberg said he didn’t know why prosecutors didn’t file the additional charges against Kelly when they first indicted him in February.

“I can’t speculate about why prosecutors do something. I deal with what they do. It’s the same facts. The same question to me, why didn’t they charge it originally, right? I don’t know why,” Greenberg said. “Maybe they’re looking for leverage. Maybe they have some other evidence that we don’t know about yet. But we expect we’ll deal with it. It’s the same facts that we know now, and it’s the same witnesses, and we expect that it’s going to be the same result. He’s going to walk out the front door.”

Kelly’s attorney also dismissed rumors that federal prosecutors are preparing to charge Kelly.

“I don’t expect anything,” he said. “If the feds indict Robert, then we’ll deal with it. I don’t know what they would possibly indict him on, but we’ll deal with it. You can’t speculate. You can’t prepare for a case that’s not there. You can’t try a case that’s not there.”

Greenberg also criticized Kelly’s accusers, claiming they recently attended an awards show, and are not acting like victims.

“This is a bunch of people who are going all over the country, getting wined and dined like they’re some kind of heroes. They’re not heroes. They’re not heroes at all, and they’re loving every minute of it,” he said. “I’ve never seen supposed victims behave like this, and the reason why they’re behaving like this is they aren’t victims.”

According to Greenberg, it’s unlikely Kelly’s trial would start until sometime next year.