WikiLeaks founder Julian Assange has blasted China as the "technological enemy" of his whistleblower website because of its aggressive Internet censorship, in comments published Thursday.

Assange has enraged the United States with his site's release of leaked diplomatic cables, and lawyers for the Australian believe efforts are under way to send him to the US where they claim he could face the death penalty.

But China, with its vast Internet censorship system know as the "Great Firewall of China," is the site's most feared foe in cyberspace, the 39-year-old told Britain's New Statesman magazine.

"China is the worst offender" when it comes to censorship, said Assange, who is on bail in Britain fighting attempts to extradite him to Sweden over claims of sexual assault.

"China has aggressive and sophisticated interception technology that places itself between every reader inside China and every information source outside China.

"We've been fighting a running battle to make sure we can get information through, and there are now all sorts of ways Chinese readers can get on to our site."

China's system of censorship is designed to filter out any information deemed sensitive or politically harmful by the country's Communist government.

Social networking site Facebook, video-sharing giant YouTube and microblogging site Twitter are among those blocked by Chinese censors.

In the interview Thursday, conducted by veteran journalist John Pilger, a prominent supporter of the Australian hacker, Assange also claimed he had files on media mogul Rupert Murdoch.

"If something happens to me or to WikiLeaks, 'insurance' files will be released," Assange was cited as saying.

"There are 504 US embassy cables on one broadcasting organisation and there are cables on Murdoch and News Corp," without going into more detail on what they contained.

Assange insists that attempts to extradite him to Sweden over allegations of sexual assault by two women are politically motivated and linked to WikiLeaks' activities.

He appeared briefly in a London court Tuesday and a judge ruled that Sweden's bid to extradite him would be heard in full on February 7-8.

The hacker has been living at the country estate of a friend in eastern England since being released on bail on December 16, nine days after his arrest by British police on a Swedish warrant.

His defence team has argued that if he is sent to Sweden he could then face extradition or illegal rendition to the US and there was a "real risk" he could face the death penalty.

Assange's British lawyer Mark Stephens accused Swedish authorities of secretly planning to extradite him to the US, in an interview with German newspaper Die Zeit on Thursday. Sweden's justice ministry denied the claim.

A US court has reportedly subpoenaed the Twitter accounts of four WikiLeaks supporters as part of a criminal investigation into the leaks. US Vice President Joe Biden has described Assange as a "hi-tech terrorist."

The whistleblower website has also released classified documents about the wars in Iraq and Afghanistan.

US soldier Bradley Manning is in military custody in the United States awaiting trial for having allegedly obtained and leaked the cables.

Assange said Thursday that he thought the US was trying to use Manning to build a case against him, but denied ever having heard of him before his name appeared in media reports.

"Cracking Bradley Manning is the first step," he continued. "The aim clearly is to break him and force a confession that he somehow conspired with me to harm the national security of the United States."