Whistleblower Edward Snowden - famous for his US National Security Agency (NSA) leaks - has claimed in a US television interview that he has "no relationship" with the Russian government and had not given Moscow any secret intelligence documents.

"I have no relationship with the Russian government at all," said Snowden in an interview with NBC News, his first on US television after a year of asylum in Russia.

"I'm not supported by the Russian government. I'm not taking money from the Russian government. I'm not a spy," he continued.

The NSA contractor disclosed the US government's use of a surveillance programs to secretly investigate on their own citizens and others around the world.

He said that he was comfortable with his decision and, despite homesickness, could sleep easily at night for trying to protect the US constitution.

"I may have lost my ability to travel, but I've gained the ability to go to sleep at night and to put my head on the pillow and feel comfortable that I've done the right thing even when it was the hard thing. And I'm comfortable with that," he added.

Secretary of State John Kerry said that Snowden should "man up and come back to the United States."

"The bottom line is this is a man who has betrayed his country, who is sitting in Russia, an authoritarian country where he has taken refuge," Kerry told CBS' This Morning show.

The whistleblower claims to have deleted classified documents before going to a Moscow airport from Hong Kong where he first sought asylum.

"I took nothing to Russia, so I could give them nothing," he said.

He added that if he "could go anywhere in the world, that place would be home" but he would not "walk into a jail cell" by entering the US without clemency.

On his Russian visa status, which expires on 1 August, Snowden said that if it "looks like it's going to run out, then of course I would apply for an extension."