Fall Out Boy’s Pete Wentz has dismissed reports his fiancee Ashlee Simpson is pregnant with his baby, calling the media scrutiny on the couple a "witch hunt".

Rocker Wentz and the pop star sister of singer/actress Jessica Simpson confirmed reports they had become engaged last week, and on Monday, American magazine Us Weekly claimed the 23-year-old was pregnant.

But Wentz insists this is untrue.

He tells MTV: "There is a witch hunt for people to be pregnant whenever they get engaged in Hollywood. This is all news to me.

"I can't wait for the story about how I'm really in a gay relationship and this is all just a cover... I mean, really, this is crazy.

"I mean we're engaged, that's true, and happy about it."