EXCLUSIVE

A former employee of R. Kelly told a grand jury the singer regularly recorded tapes of his sexual encounters with underage girls and kept them as trophies ... and they're now believed to be in the hands of the feds.

Sources directly connected to the case tell TMZ ... the ex-employee testified in front of a federal grand jury in the Northern District of Illinois Thursday, and claims to have been in possession of multiple tapes in which the singer engages in sex acts with minors.

We're told the former employee told grand jurors R. Kelly paid a large sum of cash to the employee and in return, the employee handed a tape over to the singer. We're told somehow the tape in question ended up in the hands of Cook County State's Attorney Kim Foxx.

Our sources say the ex-employee testified they gave the feds several other child sex tapes featuring Kelly.

We're told the former employee said R. Kelly's crew knew full well Kelly had a penchant for having sex with underage girls, but rather than blow the whistle on him, they actually helped the singer procure young girls.

R. Kelly's attorney, Steve Greenberg, tells TMZ, "This seems to be the same claims that were made in the state case. We will address them in court."

A spokesperson for the U.S. Attorney for the Northern District of Illinois declined to comment.

As we've told you ... the federal grand jury in IL has heard testimony from alleged victims who say the singer and his camp transported them across state lines for sex when they were underage.