WikiLeaks founder Julian Assange says a former adviser to Prime Minister Stephen Harper should face criminal charges for suggesting that the Australian whistleblower should be killed.

During an online interview with London's Guardian newspaper, Assange commented on Tom Flanagan's recent suggestion that he "should be assassinated" for his role in the public release of U.S. diplomatic cables.

"It is correct that Mr. Flanagan and the others seriously making these statements should be charged with incitement to murder," Assange told the Guardian website on Friday.

Flanagan, who previously served as Harper's chief of staff, has already apologized for the controversial remarks he made earlier this week while appearing on a political talk show.

During the show, Flanagan suggested that U.S. President Obama "should put out a contract or maybe use a drone or something" to kill Assange.

Appearing on the same program a day later, Flanagan apologized for his "thoughtless, glib remark about a serious subject."

Flanagan said he "never seriously intended to advocate or propose the assassination of Mr. Assange."

Assange has come under fire in recent days after WikiLeaks began publishing an initial wave of diplomatic cables to its website on Sunday. It plans to put 250,000 such documents on the Internet over time.

At the moment, Swedish authorities are seeking to question Assange "in connection with a number of sexual offences," according to an Interpol news release. The 39-year-old has denied that he has done anything wrong.

Additionally, the United States has made notice that it has "an active, ongoing criminal investigation" into the release of its diplomatic cables.

With files from The Canadian Press