Taking to Facebook, the US ambassador to Australia is urging Australians to cease their illegal downloads of Game of Thrones, saying that they are among the world's worst pirates of the wildly popular medieval television drama.

In a post titled "Stopping the Game of Clones", Jeffrey Bleich - himself a devotee of the HBO series - compared the rampant piracy of online thieves to the plotting and machinations of the noble houses in the show.

"Unfortunately, nearly as epic and devious as the drama is its unprecedented theft by online viewers around the world," he wrote on his official Facebook page.

"As the ambassador here in Australia, it was especially troubling to find out that Australian fans were some of the worst offenders with among the highest piracy rates of Game of Thrones in the world".

TorrentFreak, a file-sharing news website, estimated that Game of Thrones was the most pirated TV series in 2012, with one episode notching 4.28 million pirated downloads, equal to the number of broadcast viewers for that episode, Bleich said.