Pamela Anderson is planning another visit to the high-security Woolwich prison holding Julian Assange after declaring that her "heart breaks" for the WikiLeaks founder.

In a tweeted letter to the Australian prime minister and foreign affairs minister, US President and first lady, the US actress has urged Assange's home country Australia to stop him being extradited to the US.

Ms Anderson said that Assange has been subjected to "traumatic psychological torture" but that he is "hanging on like a super hero" in Belmarsh prison in Woolwich.

Assange was sent to the prison earlier this year after he was dragged out of the Ecuadorean embassy in London and sentenced to 50 weeks in prison for a bail violation.

He is currently fighting extradition to the US, where he is wanted for questioning over the activities of WikiLeaks.

This is not the first time the controversial whistleblower has received celebrity visitors in the Woolwich prison.

Singer MIA went to Belmarsh in October to see Assange and demanded his release, and back in April Ms Anderson visited him along with WikiLeaks editor Kristinn Hrafnsson.

Ahead of her latest visit, Ms Anderson said she was "extremely distressed at the thought of his declining state"

"Knowing Julian as I do he can survive this, he is strong, focused and willing to sacrifice even his life for all of us."

The former Baywatch star appealed to Australia to "protect him" as extradition is a "death trap."

"When I visit Julian in a few weeks I am very much looking forward to be able to convey to him that the tide is shifting."

In the US, Assange faces 18 charges including allegations that he conspired to break into a Pentagon computer and that we worked with former US army intelligence analyst Chelsea Manning to leak hundreds of thousands of classified documents.