IOWA CITY, Iowa — A nationwide sex trafficking ring run by a violent pimp and his associates used Backpage.com to solicit customers for prostitutes as young as age 17, advertising the women as “smokin’ hot babes,” according to a federal indictment recently unsealed in Iowa.

A 50-page indictment alleges a New Jersey man used coercion and violence to force women between 17 and 21 to act as his sex workers between November 2009 and June 2011, when investigators broke up the ring during a sting operation at a hotel in Omaha.

The man, Johnelle L. Bell, 27, was arrested in New Jersey earlier this month and has been transported to Iowa to face a 12-count indictment, which includes charges of conspiracy to commit sex trafficking and interstate transportation for prostitution. He has pleaded not guilty. Brittany Lawson, 21, who prosecutors say helped Bell manage the ring, was arrested last month in Hot Springs, Ark., and is expected to be arraigned in Iowa next week.

The indictment says their operation was headquartered in Little Rock, Ark., but workers traveled frequently, stopping in a dozen states in one two-month span last year. They posted solicitations on Backpage.com and other sites advertising the women as escorts, including their photographs, services offered and numbers for customers to call, the indictment says. “Exotic Playmate Last Night in Town!!!!” one of many such ads on Backpage.com read, telling customers the location of the Des Moines hotel where the woman was waiting, according to the indictment.

Lawson used Backpage.com to research other prostitutes for Bell who could be recruited to join the conspiracy, the indictment says.

The indictment comes as the website, owned by Village Voice Media, is under fire from critics who say it profits from sex trafficking. Critics are lobbying the company to remove ads for escorts and adult services but the company has resisted, noting it cooperates with law enforcement. Attorneys general across the country are investigating Backpage.com’s practices. Police in Detroit are investigating the slayings of four women whose bodies were found in car trunks after three of them placed online escort ads through the site.

A spokeswoman for Village Voice Media had no immediate comment on the Iowa indictment.

Bell used promises of a personal relationship and wealth to recruit young women as sex workers, including a 17-year-old homeless girl who had been working as a prostitute in Little Rock, the indictment says. Prosecutors say he used physical and psychological force to prevent them from leaving, striking them, whipping them with a belt, choking them, threatening to kill their families if they left and taking their identification documents. Bell allegedly told one prostitute to get a tattoo his nickname, “Victorious P,” as a branding strategy.

The indictment says Bell collaborated with at least three other pimps, sharing expenses for promoting their prostitutes and information about recruiting, training and law enforcement in different geographic areas. Bell would decide where his women would be sent across the country, and he had some of them seek out customers at truck stops, the indictment said.

Lawson helped Bell run the conspiracy, obtaining rental cars to transport workers and making their hotel accommodations, taking phone calls from customers, overseeing appointments to make sure money was paid and occasionally working as a prostitute herself, according to the indictment.

A magistrate judge on Monday ordered Bell detained pending trial, noting he’d served prison time for robbery in the past, traveled frequently and had no regular source of income. Bell’s attorney, public defender John Burns, declined comment. But he filed a motion Wednesday seeking Bell’s release, arguing he would show up to court hearings and “would pose no danger to the community.”

Lawson has been released on a $5,000 bond, and is scheduled to make an initial appearance in Council Bluffs, Iowa next week. Her attorney did not immediately return a phone message.

The two are charged in Iowa because Des Moines was a site where the ring did business on at least four occasions, sometimes holing up in an Econo Lodge near Interstate 35, the indictment says.