In this image from video provided by the FBI, a suspect is arrested in Washington, D.C. as part of the bureau's Operation Cross Country.

PORTLAND, Ore. (AP) - The FBI says state and federal authorities picked up seven underage girls and six adult pimps in the Portland area as part of a weekend nationwide child prostitute sting.

They also cited 14 adult female prostitutes and three customers or other associates.

The agencies did two similar sweeps last year, but Portland did not participate.

Sites of the weekend detentions were not disclosed. The seven girls were undergoing protective assessment by the Department of Human Services. The pimps were charged with a variety of crimes.

The weekend action was part of the national Innocence Lost project located in more than 30 FBI offices. The Portland office just received approval to join.

In total, the FBI rescued more than 45 suspected teenage prostitutes, some as young as 13, in the nationwide sweep.

The teenage prostitutes found in the investigation ranged in age from 13 to 17.

Meanwhile, in Memphis, Tenn., a man pleaded guilty Monday to federal civil rights charges for sex trafficking in minors. Leonard Fox faces at least 10 years in prison after admitting that he arranged for underaged girls to engage in sex for money.

"To sexually prey upon young girls in this manner for financial gain is particularly damaging to the victims and an affront to the society in which we live," said Loretta King, acting head of the Justice Department's Civil Rights Division.

Historically, federal authorities rarely play a role in anti-prostitution crackdowns, but the FBI is becoming more involved as it tries to rescue children caught up in the business.

"The goal is to recover kids. We consider them the child victims of prostitution," said FBI Deputy Assistant Director Daniel Roberts.

"Unfortunately, the vast majority of these kids are what they term 'throwaway kids,' with no family support, no friends. They're kids that nobody wants, they're loners. Many are runaways," Roberts said.

Most of the children are put into the custody of local child protection agencies.

Agents in cities from Miami to Chicago to Anchorage, Alaska took part in the operation.

Special Agent Melissa Morrow of the FBI's Washington office said the operation has put them on the trail of a particular 16-year-old prostitute they still haven't found.

Adult prostitutes arrested during the operation provided key tips about the girl, the agent said.

"She is currently 16 and started when she was 13. Now she is out there recruiting other juveniles as well," said Morrow, adding that finding the girl is "at the top of our list."

The federal effort is also designed to hit pimps with much tougher prison sentences than they would likely get in state criminal courts.

Government prosecutors look to bring racketeering charges or conspiracy charges that can result in decades of jail time.

"Some of these networks of pimps and their organizations are very sophisticated, they're interstate," said Roberts, requiring wiretaps and undercover sting operations to bring charges.

The weekend's roundup marked the third such Operation Cross Country, and is part of a broader federal program launched in 2003 to crack down on the sexual exploitation of children.