Federal prosecutors in South Dakota have charged a Wisconsin man with sex trafficking.

The U.S. Attorney's Office in Sioux Falls says 33-year-old Thomas Alexander Roberts, of Milwaukee, pleaded not guilty to transportation for prostitution, coercion and commercial sex trafficking.

The maximum penalty if he's convicted is life in prison.

Prosecutors say Roberts transported an adult female from Wisconsin to South Dakota this month with the intent of having her engage in prostitution and sexual activity.

The public defender's office in Sioux Falls representing Roberts was closed Friday and he's in custody.