American whistleblower Edward Snowden said he will return to the US from Russia to face charges of treason — but only if he can be guaranteed a fair trial.

The former National Security Agency contractor, who leaked thousands of classified documents showing massive digital snooping by the NSA — and British intelligence agency GCHQ — said he would launch a public interest defence of his actions.

He made his comments live on Skype to the New Hampshire Liberty Forum, which was heavily attended by members of the Libertarian Party, the Associated Press reported.

"I've told the government I would return if they would guarantee a fair trial where I can make a public interest defence of why this was done and allow a jury to decide," Snowden told the conference.

Information can be withheld at trials where judges agree with government lawyers that release of such information could threaten national security. Snowden is hoping for a full airing of all the issues and that he will be free to use information helpful in his defence.

He has been living in Russia for nearly three years after fleeing beyond the reach of US jurisdiction. If convicted of the US Espionage Act crimes he's charged with, he could face 30 years in prison.

Snowden's revelation of the secret program involving bulk downloads of Internet and phone records by the American and British intelligence agencies shocked people around the world and triggered a vigorous debate about the legitimate — or illegal — reach of governments battling fears of terrorism.

Snowden said some of his former colleagues at the NSA and CIA have told him the US
Constitution "doesn't really matter" concerning illegal search and privacy intrusions — though he noted that others agree with him about the importance of individual rights.

Snowden has previously spoken of making offers to the government to return home and discuss a plea deal. Former US Attorney General Eric Holder has said in the past that a plea deal with Snowden was a possibility, but the whistleblower told the BBC in late 2015 that his lawyers were still waiting to hear from someone in the government.