US prosecutors described rhythm and blues superstar R. Kelly as a vile manipulator who took advantage of his vulnerable goddaughter in closing arguments at his child pornography trial on Thursday.

Speaking in a near-monotone voice as a sex tape was played in the darkened Chicago courtroom, assistant state attorney Robert Heilingoetter pointed out each of the acts which constitute the 14 child porn charges against Kelly.

"Direction," Heilingoetter said as jurors hear the man on the tape call a naked young woman by the name of Kelly's goddaughter and command her to dance for him, saying "stand straight up baby" and "turn around".

The remainder of the 26-minute tape is even more disturbing as the man readjusts the camera again and again to capture a series of raunchy and degrading sex acts.

The girl — who prosecutors allege was Kelly's goddaughter and say was as young as 13 when the home movie was made — does not smile as she robotically obeys the commands.

"There's no exception for 'if the girl consents'," Heilingoetter reminded the jurors, before they later began their deliberations.

Kelly faces up to 15 years in jail if convicted on the 14 charges of child pornography but has pleaded not guilty in the trial which began on 9 May.

"You know what's on that tape and you know it's vile and you know it's disgusting and you know it's Robert Kelly and (his goddaughter)," Prosecutor Shauna Boliker told jurors.

But Robert Kelly's lawyers insisted he is not the man in the tape and argued the female was not in fact his goddaughter. They accused the 14 witnesses who identified the girl of lying as part of an elaborate extortion scheme.

They brandished a set of photographs showing a large black mole on the singer's back and a shot from the video where no mole is visible on the naked man's back.

"How does that mole come and go?" defense attorney Sam Adam asked. "There is no mole there and that means one thing: it ain't him and if it ain't him you can't convict."

Adam reminded the jurors that Kelly's goddaughter told a grand jury that she was not the girl on the tape and insisted she would not have kept something like that secret.

"She is a 13-year-old girl having raunchy, dirty, nasty sex ... with a superstar who's won Grammy Awards and she tells no one?" Adam asked. "You couldn't keep a 13 year-old girl's mouth quiet about having Hannah Montana tickets."

Neither the prosecution nor the defense called the girl in question — who is now 23 — as a witness.

The charges, and a series of scandals involving Kelly and underaged girls, seem to have had little impact on the popularity of the Chicago-based singer, songwriter and producer.

He has sold more than 12 million records since he was arrested in June 2002, pumping out an album a year and collaborating with everyone from Celine Dion to Kid Rock.

He has not shied away from sexually charged lyrics in the wake of the controversy and his last major tour in 2006 earned $8.3-million.

AFP