ST. PAUL  — A sex-trafficking sting conducted in St. Paul as part of a larger national effort has led to charges accusing a man of forcing a teenage woman into prostitution.

A 19-year-old woman told police that Melvin Nathaniel Stewart, 27, refused to let her out of his sight. Stewart has been charged with a second-degree offense of engaging in sex trafficking.

St. Paul police investigated the case as part of an effort to crack down on pimps and so-called “johns.” The “National Day of Johns Arrests” sting ran from Jan. 23 through last Sunday, culminating with the Super Bowl because authorities consider the game a haven for sex trafficking.

Investigators located online ads that mentioned escort services from a female who they thought looked young, the criminal complaint said. An undercover officer responded and met the 19-year-old woman, who was from Eau Claire, Wis.

When the teen agreed to have sex with the undercover officer for $100, she was arrested, the complaint said.

She identified Stewart as her pimp and told investigators he always kept an eye on her.

“She stated that she never wanted to do prostitution and was being held against her will and was happy she was in a safe place” after police found her, the complaint said.