Third R. Kelly Sex Tape Surfaces, So Claims Gloria Allred

3/11 -- Gloria Allred tells TMZ ... "R.Kelly appears to take the position that all the women who have made public accusations that he has victimized them are lying and that there are no tapes which depict him victimizing under age girls. Mr. Kelly attempts to portray himself as the victim instead of a sexual predator, but many of the women with whom he has had contact accuse him of being a predator, because they allege that he has victimized them. In addition, there is no reason to believe that Mr. Dennis has done anything wrong or that he will be prosecuted. The response by Mr. Kelly’s representative appears to be just a scare tactic to deter individuals who may have similar tapes from coming forward to provide them to me or law enforcement."

1:42 PM PT -- R. Kelly's attorney, Steve Greenberg, tells TMZ ... "R. Kelly denies that he is on any tape with underaged girls. The doubt here is self-evident, with reporting that the man on the tape kinda, sorta looks like R Kelly. That doesn’t make it him. It is not him."

Greenberg also says he wants to know what investigators will do about the fact that the Dennises were in possession of possible child pornography, asking, "Are they going to be prosecuted?" He adds, "It is obviously now just open season on R. Kelly. It is irresponsible to continue to take the speculation of every Tom, Dick and Harry, and report it as if it is fact."

Another sex tape has surfaced that purportedly shows R. Kelly with minors -- and Gloria Allred is repping the guy who claims to have found it and turned it over to cops.

Allred just held a press conference in NYC, where her client, Gary Dennis, came forward to explain how he found the tape, and why he's speaking out now.

Dennis, who says he has no connection to R. Kelly whatsoever, claims he recently found this new sex tape while going through old VHS tapes of his own. He says he initially discovered the tape as a "sports tape," but says it also had R. Kelly's name on it.

Dennis goes on to say that he thought the R. Kelly part of the tape would feature a concert of his, but later discovered it was a sex tape as he continued to watch past the sports content. He says he doesn't know how this tape turned up in his possession but says he watched it and saw R. Kelly engaging in sex acts with what he perceived to be underage black girls ... more than one.

Dennis didn't go into much detail about what he saw on the tape but did say that the girls on camera were doing and saying things based on R. Kelly's instructions. Dennis also says the girls appeared to be underdeveloped and that the only man on tape -- who he claims looked a lot like R. Kelly -- seemed to be in charge of the camera.

The guy says the tape appears to have been produced in the 1990s ... adding there's no indication of where it was filmed.

Allred says they've turned over the sex tape to law enforcement officials from U.S. Attorney's Office for the Eastern District of New York. She wouldn't comment one way or another on whether she'd personally seen this new tape herself. However, Allred says she believes more tapes of R. Kelly are in circulation.

This tape would be the third one handed to law enforcement in the last month. Attorney Michael Avenatti has already turned over 2 tapes to prosecutors in Chicago ... one of which prompted the 10 count indictment against R. Kelly for aggravated sexual abuse.

Speaking of Avenatti, he appears to have responded to Allred's press conference ... and seems to be casting doubt on the veracity of her client's claims.

BTW ... Allred already reps a number of R. Kelly accusers, including two women who say he targeted them after a Baltimore concert in 1995. One of those women, Latresa Scaff, says R. Kelly had sex with her without her consent in a hotel room ... this after he'd already plied the then-underage girls with alcohol and drugs at an after-party following his concert.

Allred says a witness has come forward to corroborate the Baltimore women's accounts, and all three of them have spoken to the U.S. Attorney's Office for the Eastern District of New York.