WIKILEAKS founder Julian Assange has urged US officials to leak secret documents on drone strikes, saying that the broad discretion to kill citizens shows a "collapse" in the American system.

Mr Assange, who has angered US officials by releasing thousands of secret memos, used a rare US television appearance to condemn President Barack Obama's controversial green light to kill American citizens who conspire with al-Qaida.

"I can't see a greater collapse when the executive can kill its own citizens arbitrarily, at will, in secret, without any of the decision-making becoming public," Mr Assange told the HBO talk show Real Time with Bill Maher.

"That's why we need organisations like WikiLeaks. I encourage anyone in the White House who has access to those rules and procedures, work them on over to us. We'll keep you secret and reveal it to the public."

Mr Assange spoke to host Bill Maher, a supporter of WikiLeaks, by video link from Ecuador's embassy in London, where he has been holed up since June to avoid extradition to Sweden. Britain has refused him safe passage to Ecuador.

Swedish authorities say they want to question Mr Assange over allegations of sex crimes. The former computer hacker says he fears Sweden will extradite him to the United States over WikiLeaks's massive release of sensitive documents.

Bradley Manning, a young army intelligence analyst in Iraq, was arrested in May 2010 over suspicions he handed diplomatic correspondence and other data to the website. He faces life in prison if convicted by a military tribunal.

NBC News published an unclassified document by the Justice Department this week indicating that senior al-Qaida operators may be lawfully killed, even if they are US citizens and are not shown to be actively plotting an attack.

The Obama administration called strikes legal, ethical and "wise," and vowed to provide lawmakers with access to secret documents that outline the legal justifications for drone strikes.

Human rights groups voiced outrage in September 2011 when a US drone strike in Yemen killed radical preacher Anwar al-Awlaki and Samir Khan, editor of an al-Qaida magazine. Both were US citizens who had never been charged with a crime.