In a shocking discovery, law enforcement officials rescued nearly 170 victims of child sex trafficking, many of whom had never been reported missing as part of an annual nationwide crackdown, the FBI said Monday.

In addition to the children, 281 pimps were arrested during the same period on state and federal charges, USA Today reports.

"These are not faraway kids in faraway lands," FBI Director James Comey said in announcing the annual enforcement push known as Operation Cross Country. Instead, he added, "These are America's children."

This operation marks the eighth week-long operation, which takes place in 106 U.S. cities. Thus far, 3, 600 children who have been sexually exploited have been rescued.

"I hate that we have to do this work - hate it," Comey continued. "I love the people who've devoted their lives to doing this work. There is no more meaningful work that the FBI participates in than rescuing children."

He said the operations were designed to "crush these pimps" and show that children are not for sale. They are also intended to rescue children who are being trafficked on street corners, in truck stops and, increasingly, on the Internet, where pimps advertise and arrange sexual encounters.

One disturbing trend, Comey said, is that many of the children who were recovered were never reported missing in the first place, whether by parents, guardians and the entire child welfare system designed to protect them.

"No one is reporting them missing. Hence, no one is looking for them," said John Ryan, CEO of the National Center for Missing and Exploited Children. "But for operations like this, these children likely would never have been found."

"We cannot find them if no one reports them missing," Ryan said.

The operation, which has taken place annually since 2003, covered 106 cities, including several in Georgia, Texas, and Oregon.

Investigators targeted truck stops, casinos, websites and streets to make initial arrests for prostitution or solicitation. Information gathered during those arrests usually brought forth details leading to larger organized prostitution rings - some of which were operating across state lines, authorities said.

Operation Cross Country is part of the Innocence Lost National Initiative, established in 2003 by the FBI's Criminal Investigative Division, in partnership with the Justice Department and the national center.