Federal authorities arrested 120 accused sex traffickers and rescued 84 "sexually exploited juveniles" - including an infant just 3 months old - after a nationwide sweep involving about 500 law enforcement agencies, the FBI announced.

The operation, dubbed "Cross Country XI," involved 58 FBI field offices as well as hundreds of local and state law enforcement agencies in an investigation that took place in hotels, casinos, truck stops, street corners and online, the FBI said. Authorities from Canada, Britain, Thailand, Cambodia and the Philippines also were involved.

The 3-month-old girl and her 5-year-old sister were rescued in Denver after a friend of their family had offered to sell the two children for $600, the FBI said in a statement. Officials are working with a protective services agency to house the two girls; a suspect has been arrested.

The sweep was the 11th iteration of Operation Cross Country, part of the FBI's Innocence Lost National Initiative, which began during the George W. Bush administration. Since 2003, that initiative has led to the identification of more than 6,500 child victims and locations, according to agency statistics.

But some critics have pointed out that the sweeps tend to result in hyperbolic news releases and pronouncements. The Washington Post's Glenn Kessler, for instance, has written that "while Operation Cross Country is supposed to focus on juveniles, in recent years it ended up yielding at least five times as many adult sex workers as children."

As Kessler noted in a Fact Checker column two years ago:

"In some cities, the ratio is startling. During the 2015 operation, for instance, the Sacramento FBI field office announced that it had located five underage children, seven pimps and also arrested 90 adults 'for various offenses including probation violations and prostitution-related charges.' In Iowa, 10 adults were arrested (five for prostitution and five for soliciting sex), but no minors or pimps were found. In Mississippi, two minors were found, 24 adults were arrested on prostitution and other charges - and no pimps were arrested.

"Moreover, the FBI numbers are based on initial reports but apparently are not updated for actual charges."

Kessler added that "government officials appear to believe they can boost their success rate by slapping the word 'sex trafficker' on adults who have been arrested even though such charges have not - and could not - be brought in a court of law. The goal of rescuing children from the sex trade is laudable, but the effort is undermined when the statistics are cooked."

The FBI did not include the numbers of people arrested besides the sex traffickers in its announcement this week, and the agency did not respond to an immediate request for that statistic.

The agency did note, however, that the average age of victims rescued in the latest sweep was 15.

Video released by the FBI shows agents scouring Backpage.com and other Web advertisements, apparently trying to identify underage women, and staking out hotels.

"We at the FBI have no greater mission than to protect our nation's children from harm," FBI Director Christopher Wray said in a statement. "Unfortunately, the number of traffickers arrested - and the number of children recovered - reinforces why we need to continue to do this important work."

He added that the operation "isn't just about taking traffickers off the street. It's about making sure we offer help and a way out to these young victims who find themselves caught in a vicious cycle of abuse."

Indeed, in the agency's video, authorities are shown attempting to help the victims.

"I wanted to make sure that y'all knew that there are resources out there," a specialist tells one apparent victim. "If you want to get back to California, like today, we can do that."

The FBI said that minors recovered during its sweeps "are offered assistance from state protective services and the FBI's Victim Services Division. Depending on the level of need, victims are offered medical and mental health counseling, as well as a number of other services."

Any child 17 or younger who is involved in a commercial sex act is a victim of sex trafficking, according to the National Center for Missing and Exploited Children.

The NCEMC noted that children with "increased vulnerabilities" are at greater risk of being trafficked, including those who have experienced sexual abuse, assault or rape previously, run away frequently and have substance abuse issues. Also vulnerable are those who identify as lesbian, gay or transgender and have been kicked out or shunned by their families. An estimated 1 out of 6 runaways reported to the NCMEC are thought to be victims of sex trafficking.

John Clark, chief executive and president of the NCMEC, said in a statement that he hopes that the operation "generates more awareness about this crisis impacting our nation's children."

According to Thorn, a nonprofit dedicated to combating child sexual exploitation, black and Latino children are disproportionately represented among the victims. Studies have shown that 50 to 90 percent of child sex trafficking victims have been involved in the child welfare system, it said.

Staca Shehan, an executive director at the NCMEC, said there are no reliable statistics for the number of children who are sex-trafficked nationally each year. She said that awareness of the problem domestically has been growing but that technology has "dramatically changed the landscape."

"Several years ago, the vast majority of children we'd see were recruited in malls, bus stops, train stations, in or around schools, foster homes, and they were sold at motels, hotels, casinos, truck stops and on the street," she said. "And while all of that is still true, we have seen the Internet become the number one place that children are approached or recruited, a way in which they're being controlled through the technology and where they're being sold."

In announcing the results of its latest sweep, the FBI spotlighted a handful of cases - including one in El Paso, where an undercover agent responded to an online ad for entertainment.

Shortly thereafter, the agent met with a 21-year-old female, who offered a fee of $200 to engage in sexual intercourse with her and another female, the 16-year-old victim. Further investigations revealed that a second adult female drove the minor and the 21-year-old to the undercover agent's location. Both female subjects have been arrested on federal charges.

The FBI also shared the account of a sex-trafficking victim, identified only as Ali, who it described as a Philadelphia native with a master's degree.

Ali was once trafficked as a prostitute after becoming addicted to heroin. She now works at a drug-treatment center.

"It can happen to anybody," she said in a video distributed by the FBI.

She described how her addiction made her vulnerable to traffickers.

"In the beginning, it's easy for them to manipulate you when you have nothing and they're literally providing you with everything," she said. "If they would be physically abusive toward you, they would remind you that they were your primary source of income, your primary place to have a roof over your head, to feed you. So even though that part of it was there, it's kind of like you were willing to sacrifice - I was willing to sacrifice - enduring that because without that person, I thought I had nothing."