In a post on RevolutionMuslim.com, Trey Parker and Matt Stone have been told their portrayal of the religious figure in a recent episode went too far - and they have now become targets.
In the episode, a cartoon Muhammad dresses up in a bear suit.
The post from the Islamic group references Dutch filmmaker Theo Van Gogh, who was shot by fundamentalists who objected to a movie he made about the treatment of Muslim women.
The post reads, "We have to warn Matt and Trey that what they are doing is stupid and they will probably wind up like Theo Van Gogh for airing this show."
Stone and Parker have yet to respond to the warning.