When the Federal Bureau of Investigation conducted a nationwide sweep in late July to fight child prostitution, the agency boasted that "Operation Cross Country" had successfully rescued 105 sexually exploited children.

But the National Center for Missing and Exploited Children, which partnered with law enforcement for the sweep, says that some of those rescued children may now end up behind bars.

"If there is nowhere to hold them, and nowhere safe for them to go, law enforcement has no alternative," says Staca Shehan, the director of the case analysis division at the center. "If they aren't placed in a juvenile detention facility, the child could run back to the prostitution scenario."

To avoid this, police charge the children with prostitution and place them in a detention facility until housing elsewhere becomes available, according to Shehan.

FBI spokeswoman Whitney Malkin confirmed to U.S. News that some of the child victims rescued by Operation Cross Country could be detained, though she called such instances "rare" and said many more children would be placed in safe housing by FBI Victim Specialists.

"Detaining victims... falls far short of ideal," she says, but noted "the infrastructure to support the range of services just isn't there in many places."

In a May report, anti-sex trafficking group Shared Hope International said government agencies and law enforcement needed to do better at placing child sex trafficking victims in domestic shelters or providing other services. The group urged better communication between service providers, more training for law enforcement on trauma responses and more diverse options for placement.

Sienna Baskin at the Urban Justice Center, a New York-based advocacy group that works with sex trafficking victims, says the FBI should also provide more clarity on how many minors were detained in this particular sweep and where the others were placed.

"It seems like they're treating the arrest of minors as an acceptable collateral consequence of this operation. But arrest is a very traumatic experience that can lead to abuses for both adults and minors," she says.

The FBI was not able to immediately provide the number of detained children, or the number of female sex workers arrested in the sting – another concern of anti-trafficking groups about Operation Cross Country.

In their July newsletter, the Chicago Alliance Against Sexual Exploitation said it believed police had used the sting as an opportunity to arrest more adults in prostitution. Stephanie Richard, policy and legal services director at the Los Angeles-based Coalition to Abolish Slavery and Trafficking, says her group is also concerned about arrests of female sex workers in the sting because "we have not received assurances from those conducting these raids about whether or not adult women could be victims as well."

In past sweeps, the FBI released the numbers of prostitutes it had arrested, but it no longer does so. Local media reports on the sweep aggregated by feminist blogger and activist Emi Koyama suggest the number of sex workers arrested in Operation Cross Country may have been as high as 1,000.

But Shehan insists the "number one focus" of the operation was to recover minors, not arrest prostitutes. "Will [the FBI] leverage the interaction if they encounter an adult? Absolutely," she says. "But recovering juveniles from trafficking is the highest priority."