Another US Republican politician is under fire for remarks about rape, in this case saying, "some girls, they rape so easy".

Wisconsin representative Roger Rivard first made the statement when discussing the case of a local high school student who'd been charged with sexual assault for having sex with an underage girl.

The Chetek Alert paper quoted him in December as saying his father had warned him "some girls rape easy" - meaning that some girls could decide later that sex wasn't consensual.

He doubled down on the comments in an interview with the Milwaukee Journal Sentinel Wednesday, saying he took his father's warnings about the dangers of premarital sex seriously.

"He also told me one thing, 'If you do (have premarital sex), just remember, consensual sex can turn into rape in an awful hurry,"' Rivard told the paper.