A 15-year-old boy has been charged with raping a 47-year-old woman over a several-month period at a home in southeastern Minnesota, authorities said Tuesday.

"Coercion was used" by the boy on his victim from September until January, said Chris Cichosz, chief deputy with the Winona County Sheriff's Office.

"I believe [the assaults] would have continued if the victim did not report it" to authorities last week, said Cichosz, who added that the woman had no mental or physical challenges that would have made her vulnerable to the assaults.

The boy remains in custody on a charge of third-degree criminal sexual conduct. The case was transferred to nearby Olmsted County for prosecution because of a conflict in Winona County. Officials have yet to say anything further about the conflict.

Because of the defendant's age, authorities are not releasing his identity. Cichosz declined to say how the boy and the woman knew each other.

All of the assaults occurred in the residence, located in a rural area about 10 miles south of Winona, the chief deputy said.

Cichosz said investigators are unsure whether there are other victims. "That's another reason we're continuing with this investigation," he said. "It's a unique case."

Paul Walsh • 612-673-4482