WASHINGTON (AP) — More than 600 adults have been arrested and 47 children rescued in a three-day roundup targeting people who force children into prostitution.

The FBI said the roundup by federal, state and local law enforcement occurred in 29 cities, adding that the raids dismantled 12 large-scale prostitution operations run through call services, truck stops, casinos and Web sites.

The Indianapolis Police Department and Michigan State Police were among the agencies participating in Operation Cross Country II. There was no immediate word on what, if any, arrests had been made in either Michigan or Indiana.

A number of Chicago-area agencies also were involved, including the Cook County Sheriff's Office and suburban authorities in Gurnee and Mundelein.

At a news conference announcing the results of the sweep, FBI Deputy Director John Pistole said the arrests were made possible by intelligence gathered during a similar series of raids in June.

"Sex trafficking of children remains one of our most violent and unconscionable crimes in this country," Pistole said.

The 47 rescued children ranged in age from 13 to 17, and all but one are female.

Of these, Pistole said, 10 had been reported to the National Center for Missing and Exploited Children.

"In June, at the announcement of Operation Cross Country One, I made a comment that millions of Americans think this is the kind of problem that only happens somewhere else — Southeast Asia, Central America, Eastern Europe," said Ernie Allen, the center's executive director.

"Operation Cross Country Two is the latest evidence that this is a problem that’s happening on Main Street USA."

A total of 642 people were arrested. The FBI says they include 73 pimps and 518 adult prostitutes.

The operation was part of a larger, five-year initiative that has led to the recovery of 575 children and the dismantling of 36 criminal operations since June 2003.

Child prostitution has taken on a new urgency in recent years with the growth of online networks where pimps advertise the youngsters to clients.

The FBI generally gets involved in child prostitution cases that cross state lines.

A University of Pennsylvania study estimated that nearly 300,000 children in the United States are at risk of being sexually exploited for commercial purposes.

"Make no mistake, the minors who were interdicted as a part of this operation are victims of the most extreme form of sex trafficking," said acting Assistant Attorney General Matthew Friedrich.

"It sadly remains the case even now in 2008 that there remain instances of children in the United States manipulated into prostitution by pimps willing to make a fast buck based on the most vulnerable among us," he said.

SBT24/7 News contributed to this report.