In a horrific incident, a US couple is facing charges for forcing their four underage daughters into performing sexual acts for pornographic filmmakers. The enormity of the horror faced by the four girls came to light when investigators found the "deplorable" conditions under which the girls where living inside a trailer in Tennessee, U.S. Reports say the girls, aged five to 16, were taken around town, to sex customers.

Ronnie Lee McCall, 61, and Connie McCall, 40 have been charged by the police. Judicial district attorney general Tony Clark, told WATE TV that it was one of the worst cases he had seen. The parents face up to 30 years in jail if found guilty.

"When you have parents allegedly making money off their kids through pornography and exploitation, even after 20 years, it's one of the worst cases I've ever seen," he said.

After questioning the children, Johnson City Police confirmed that the kids had been sold to create child pornography.

"There was money that changed hands between the individuals that were taking pictures and the parents," District Attorney Tony Clark is reported to have told WATE TV.

"The children said that they had been taken to various locations and performing sex acts with an adult," he said.

The sordid tale of suffering the girls underwent came to light after information received by the US attorney's office said the father had taken one of his daughters to appear in a porn film. It was reported that the maker of the porn film later committed suicide.

Police investigator Debbie Dunn said that the four girls were found in an "inexcusable" condition.

"The amount of tooth decay (the six-year-old had) was extremely painful. She had black teeth, and holes in all the teeth, just really inexcusable," Ms Dunn said.

The father, Ronnie Lee McCall, is reported to have pleaded not guilty while the mother, Connie McCall, will appear in court on Wednesday.

Reports said the girls are now recovering in the care of child protection services.