WASHINGTON » Nearly 170 victims of child sex trafficking, many of whom had never been reported missing, were rescued in the last week as part of an annual nationwide crackdown, the FBI said Monday.

Besides the 168 children rescued from the sex trade, 281 pimps were arrested during the same period on state and federal charges.

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

This is the eighth such week-long operation, which this year unfolded in 106 cities. The FBI says nearly 3,600 children have so far been recovered from the street.

"I hate that we have to do this work — hate it," Comey said. "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 challenge, officials said, is that many of the children who were recovered were never reported missing in the first place — 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."

He said better laws were needed to require child welfare service to report children who disappear. Right now, he said, only two states have laws requiring agencies to report children missing from their care. There is no national, uniform standard.

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

Though this operation is the FBI’s eighth of its kind, Comey said this year featured the highest number of participating cities. But he said the biggest change was the increasing prevalence of children being sold online rather than on street corners.