Edward Snowden, exiled to Moscow after leaking classified documents, is to vote in the US presidential election.

But the whistleblower, who lives in Moscow after leaking classified US National Security Agency (NSA) documents without permission, has refused to say if he will be voting for Republican candidate Donald Trump or Democratic nominee Hillary Clinton.

Speaking at a conference in Athens by video link from Moscow, Snowden said: "As a privacy advocate, I think it's important for me ... that there should never be an obligation for an individual to discuss their vote. And I won't be doing so with mine."

Image: Snowden speaks via video-link during the conference

He added: "What I will say about the candidates is that I'm disappointed we're not hearing much about the constitution in this election cycle. We're not hearing very much about our rights."

The 33-year-old was speaking ahead of the opening of a film about him at the same time as a committee of senior US politicians denounced him as a "serial exaggerator and fabricator" and argued he does not fit the profile of a whistleblower.


US Charges Snowden With Espionage

The Republican-led committee released a three-page document of its two-year investigation into how the NSA employee revealed that his employer had, among other things, stored the phone records of millions of Americans.

The revelation launched a furious debate about privacy versus a government's ability to have the tools to fight terrorism.

The USA Patriot Act was amended last year so that such documents could not be stored.

Image: A woman holds up a sign at a support rally in New York for Snowden

Separately, all members of the committee sent a bipartisan letter to President Barack Obama on Thursday urging him not to pardon Snowden.

The letter said: "Mr Snowden's claim that he stole this information and disclosed it to protect Americans, privacy and civil liberties is undercut by his actions.

"Rather than avail himself of the many lawful avenues to express legal, moral, or ethical qualms with US intelligence activities, Mr Snowden stole 1.5 million classified documents from National Security Agency networks."