A 13-year-old California girl hung herself, leaving a letter for her father that said she couldn’t take being bullied anymore, Dec. 4, 2017. This picture is for representational purpose only. Pixabay

During FBI's annual law enforcement action — Operation Cross Country — that aims to rescue underage victims of sex trafficking, Denver's Rocky Mountain Innocence Lost Task Force rescued the youngest victim, a three-month-old girl and her five-year-old sister on Oct. 13, the Bureau said Wednesday.

A friend staying with the family of the girls made a deal with an undercover task force officer to sell them in exchange for $600. He was arrested.

The FBI is coordinating with Colorado’s Child Protective Services to conduct a forensic interview and also to ensure that the girls are living in a safe environment, according to a news release by FBI.

The FBI is working with Colorado’s Child Protective Services to conduct a forensic interview and make sure the children are living in a safe environment. The FBI did not release where in Colorado the arrest had taken place.

"The threat of child sex trafficking is something the FBI works on every single day," said Calvin Shivers, special agent in charge of the Denver Division, according to the FBI website.

He added that the Operation Cross Country gives the bureau the opportunity to educate the general public of this vicious cycle. He admitted that although "the focused law enforcement action has 'an immediate impact' of recovering a significant number of juvenile victims," a lot more has to be done to identify and recover more such child trafficking victims.

The FBI recovered 84 sexually exploited juveniles and arrested 120 traffickers during the four-day action, which involved 55 FBI field offices and 78 FBI-led Child Exploitation Task Forces.

The arrests of the traffickers came after hundreds of law enforcement personnel took part in sting operations in hotels, casinos, truck stops. They also searched for social media sites frequented by pimps, prostitutes, and their customers, the FBI website reported.

Wyoming and Colorado led the most rescues across the U.S., the FBI said during a press conference Wednesday. However, District Attorney of Arapahoe County in Colorado, George Brauchler, said that he didn't believe the high number of arrests were due to an epidemic problem of sex trafficking in Colorado, 9News, an NBC-affiliate reported.

"I just believe that we have a kind of partnership and a unique environment of experts who are willing to put themselves on the line to rescue as many as possible and that’s how you get these phenomenal numbers," Brauchler said. This perception was agreed upon by FBI Assistant Special Agent in Charge Todd Pooler as well.

"It is because we devote a lot of resources to this initiative and we have some very talented investigators and other individuals that bring this together and work around the clock to rescue these kids," Poolers said.

Operation Cross Country, which began in 2003, is part of the FBI’s Innocence Lost National Initiative. Since its inception, it has been responsible for identifying and recovering more than 6,500 children from child sex trafficking and the prosecution of traffickers. More than 30 of those traffickers have received life sentences for their crimes, the FBI website said.