Australian voters are the only ones that can save Julian Assange, his mother says.

Christine Assange's fears for her son's safety have intensified after a leaked confidential email indicated US authorities had drawn up secret charges against the founder of the whistleblowing website WikiLeaks.

WikiLeaks began publishing emails from the US-based global intelligence company Stratfor on Monday, including one from the company's vice president for intelligence that alleges secret US charges against the 40-year-old Australian have been made.

"We have a sealed indictment on Assange," Fred Burton's email to colleagues on January 26 last year says.

The Australian government this week said it was not aware of any charges by the US government against Mr Assange.