NEW YORK (AFP) - Amnesty International, Human Rights Watch and the US group ACLU launched a campaign on Wednesday (Sept 14) to push President Barack Obama to pardon Edward Snowden, the fugitive NSA whistleblower living in Russia.

The campaign's main prod is an online petition urging Mr Obama to give Snowden amnesty before his term ends in January.

The petition, at pardonsnowden.org, has already been signed by high-profile lawyers and celebrities including writer Joyce Carol Oates and actor Martin Sheen.

The chances of a pardon appear slim for Snowden, a former contractor for the National Security Agency who released thousands of classified documents in 2013 revealing the vast US surveillance put in place after the Sept 11 attacks.

The US authorities charged Snowden with espionage and theft of state secrets after he gave the documents to journalists Glenn Greenwald, Laura Poitras and Ewen MacAskill. He faces up to 30 years in prison.

Considered a traitor by some and a hero by others, the 33-year-old fled to Hong Kong, where he hid among Sri Lankan refugees in cramped tenements, and later received political asylum in Russia after the United States revoked his passport while he was en route to Ecuador.

In July, the White House rejected a petition to pardon Snowden that had garnered more than 160,000 signatures, saying he should be "judged by a jury of his peers".

Mr Anthony Romero, executive director of the American Civil Liberties Union (ACLU), said on Wednesday that although the White House greeted the campaign to pardon Snowden with "not a very positive reaction" initially, "we think it will change with the public's response" to the petition.

Snowden and his supporters argue that although he stole information, the revelations have benefited the public because they led to improved privacy protection laws.

In a videoconference on Wednesday, Snowden reiterated that he could not receive a fair trial in the United States under the Espionage Act.

"It does not permit a whistleblower defence," he said.

"The law does not distinguish between those who give free sensitive information to journalists and spies who sell it to foreign powers." Snowden himself called on Mr Obama for a pardon in comments published by Britain's Guardian newspaper on Tuesday, arguing that it had been morally "necessary" to shine a light on mass surveillance.

"If not for these disclosures, if not for these revelations, we would be worse off," he told the paper in a video-link interview from Moscow on Monday.

"Yes, there are laws on the books that say one thing, but that is perhaps why the pardon power exists - for the exceptions, for the things that may seem unlawful in letters on a page but when we look at them morally, when we look at them ethically, when we look at the results, it seems these were necessary things," he said.

Snowden insisted he had widespread support, saying the "public, by and large, cares more about these issues far more than I anticipated". The launch of the rights groups-led campaign came after the release of the Oliver Stone film Snowden, which his supporters hope shines a kind light on the whistleblower.

The movie's anti-establishment director called for a pardon at the Toronto film festival last week during the screening of his espionage thriller biopic.

"We hope that Mr Obama has a stroke of lightning and he sees the way," Stone said.

Ms Sarah Harrison, a representative of the website WikiLeaks who helped Snowden flee Hong Kong and seek refuge in Russia, said although she hopes the film will help rehabilitate him, she agreed an amnesty is unlikely.

"That would be lovely if it came," she told AFP last week. "I would be very surprised if it does."

Snowden's residency permit in Russia runs out next year.

"Then the question comes up again of where he can be safe. Obviously, he'd love to go back home," said Ms Harrison, director of the Courage Foundation, which helps Snowden and other whistleblowers.

Alternatively, "he'd really like asylum in a number of other countries, some European countries", she added.

"Maybe the situation will have changed in some of those, but sadly so far he's always been denied."