Jane Lynch has slammed Sarah Palin as "bats**t crazy" during a conference speech.

The 'Glee' actress - who plays Sue Sylvester in the FOX musical drama - joked that she had convinced the controversial politician to appear as a guest star in the series, singing an "original tune" written by the star.

She said: "Though not firm as of yet, we are pretty sure we got Sarah Palin to do a guest spot on 'Glee'. She'll be singing an original tune that I penned. It's called, 'Look at Me, I'm Bats**t Crazy'."

"I feel pretty good about these changes."

Jane also took a comical swipe at her 'Glee' co-stars - including Matthew Morrison, Lea Michele and Dianna Agron - joking that she doesn't think any of the cast are "real Americans".

Speaking at the Wall Street Journal's D: All Things Digital conference, she said: "I'm launching a Fox News investigation into the young and fresh-faced cast of 'Glee'. I have some inside information and I don't believe any one of them are real Americans."