British comedian Russell Brand has compared media mogul Rupert Murdoch to Nazi leader Adolf Hitler in an online rant.

The Forgetting Sarah Marshall star launched the scathing attack after the Sun on Sunday published a story claiming that Brand had cheated on his girlfriend Jemima Khan with model Sophie Coady.

The 38-year-old has fiercely denied the allegations.

In the piece published by the Guardian, he branded Murdoch "an animatronic al-Qaida recruitment poster".

"In the general scheme of things it might not seem like a big deal. That's because it isn't to anyone, except me or my girlfriend," he wrote.

"The pain, disruption and distress [this caused me] is a pale liver-spot on the back of Murdoch's glabrous claw. Rupert Murdoch, an animatronic al-Qaida recruitment poster referred consistently to his pride in [his newspaper] the Sun as 'a trusted news source'.

"Trusted is the word he used, not trustworthy. We know the Sun is not trustworthy and so does he. He uses the word 'trusted' deliberately. Hitler was trusted. It transpired he was not trustworthy."

Brand went on to claim that the Sun On Sunday was trying to bully him. He also criticised the now defunct News of the World.

"[Murdoch's newspaper] loves me when I'm a prattling, giggling, Essex boy 'Sh**ger of the Year', when I'm in my proper place, beneath vacuous headlines. But if I use my glistening podium to talk to the people I grew up with, or signed on with or used drugs with, vulnerable, overlooked ordinary people, people that can't sue them as I can, then out come the fangs."

In November, Brand hinted that he was considering taking legal action in a series of tweets.

"Total lies in about me in today's Sun from the paper that dishonoured the tragic dead at Hillsborough and desecrate the dead themselves," he said.