Pedophilia in the U.S. is "unprecedented" and has reached an almost "epidemic level," according to assistant director of the FBI's Criminal Investigative Division Joseph Campbell.

Although the FBI rescued 600 children last year, the FBI believes that tens of thousands of children are still being sexually exploited. Hundreds of children are sold every night for sex, the BBC reported in an investigative piece on child sex trafficking in the U.S.

"The level of pedophilia is just unprecedented right now," Campbell said. "We have so many cases constantly of individuals in all walks of life, from the very wealthy … to all other levels engaged in child pornography, child exploitation … it just seems to be almost an at epidemic level."

The vast majority of the children trafficked in the U.S. are not Mexican or Central American, but are American.

Women from the East Coast to the Midwest tell "frighteningly similar and horrific stories," reported the BBC. "Neglected, abused, exploited and often ignored starting from a young age — sometimes even prosecuted by the very people who should have protected them."

Girls are manipulated and taken advantage of before being trafficked, according to Jenny Gaines, who works at Breaking Free, a Minnesota-based advocacy group that helps former sex workers.

Half the women at Breaking Free's support group were under 18 when they were first sold for sex, and many were not much older than 18, reported the BBC.

One woman said "when [her abuser] actually found out how old I was [14] it didn't stop him ... he wanted me even more."

One woman the BBC spoke to was five months pregnant and still on the streets. She said she "was groomed from age 12 by a neighbor, who enticed her with a garage full of toys and games. He offered her money for topless photos," reports the BBC.

"I see more and more younger girls out here now and it's really sad," she said. "It's not a choice. At 12, it was not a choice."