Prostitution rings from New York to Hawaii forced more than 30 children as young as 12 to have sex at truck stops, hotels and brothels, Attorney General Alberto Gonzales said Friday, announcing a government crackdown.

Nineteen people have been arrested among 31 who have been indicted for sexual trafficking in children, taking minors across state lines for prostitution and other crimes, Gonzales said.

The indictments, in Michigan, New Jersey and Pennsylvania, target the purported operators of four child prostitution rings. Some of the children had been reported missing or had run away because they had been abused at home, FBI assistant director Chris Swecker said.

"The abhorrent acts alleged in these charges include children being herded around the country as sex slaves, forced to work as prostitutes in brothels and at truck stops, and beaten at the hands of pimps and peddlers," Gonzales said at a Justice Department news conference.

The heightened federal interest in stopping child prostitution is critical since pimps frequently take children from one state to another, making it harder for local police to stop them, said John Rabun, vice president of the National Center for Missing and Exploited Children. "If you're bright as a pimp, and thank God a lot of them aren't, you move them every two to three weeks," Rabun said.

A grand jury in Camden, N.J., indicted eight people Wednesday on charges that they conspired to recruit girls to be prostitutes in Atlantic City, N.J., Las Vegas and New York, according to court documents. The defendants managed a prostitution ring that also extended to Florida, Georgia, Massachusetts, Pennsylvania and the District of Columbia, the indictment said.

Matthew Thompkins and five others arrested Sunday are in custody in New Jersey. Thompkins had a central role in the conspiracy, the indictment said.

In Detroit, a grand jury charged four Ohio residents with forcing two girls, 14 and 15, to have sex at a truck stop in Michigan. The girls had been held as virtual prisoners in Toledo, Ohio, where they were told to address one defendant, Deric Willoughby, as "Daddy," and taken to hotel rooms for prostitution. Their payments were eventually turned over to Willoughby, the indictment said.

Another defendant, Richard Lamar Gordon, is identified in the indictment as a truck driver who took the girls from a Sears parking lot in the Toledo area to the Michigan truck stop and had sex with one of them. He has not been arrested.

A second indictment in Michigan charges Robert Lewis Young and two other men with prostitution, child pornography, money laundering and drug and weapons violations. Young's organization did business in Michigan and Hawaii, prosecutors said.

In Pennsylvania, 16 people have been charged for their roles in taking girls as young as 12 to work as prostitutes at truck stops in the Harrisburg area as well as Washington and Toledo. The defendants also allegedly gave and sold child and adult prostitutes to each other for personal use, prosecutors said.

Domestic child prostitution cases have been a federal law enforcement priority since 2003 with the advent of the Justice Department's Innocence Lost Initiative. When he became attorney general in February, Gonzales said he would focus on reducing all forms of human trafficking.

Several federal laws ban sexual trafficking in children, including one that specifically applies to taking minors across state lines to engage in prostitution.

There have been more than 500 arrests, 70 indictments and 67 convictions in such cases since 2003, Gonzales said.