NSA whistleblower Edward Snowden claimed he took no secret files to Russia with him when he fled Hong Kong for Moscow in June.
The ex-analyst, who revealed the extent of US government programmes to spy on its own citizens, has told the New York Times he gave all the papers he had to journalists in Hong Kong, keeping no copies.
He added that no files had been passed to China.
The US wants Snowden extradited to face trial in America, but Russia has refused, instead granting him temporary asylum in the form of a one-year visa.
Snowden told the NYT: "What would be the unique value of personally carrying another copy of the materials onward?
"There's a zero per cent chance the Russians or Chinese have received any documents."
The NYT said it interviewed Snowden over encrypted channels over a number of days.
His leaks include detailed information on Prism and XKeyscore, both NSA initiatives to gather data from millions of people's emails, browsing histories and webchats, as well as showing how the USA spied on other governments.
Earlier this week at IP Expo, America's former most wanted hacker, Kevin Mitnick, said Snowden should not have revealed the country's international spying activities.
"He's a rogue agent who revealed the wrongs the government did against the American people. Where I think he crossed the line was when he revealed our operations against other allies like the UK - you just don't do that," he told an audience.
But he added that Snowden might have little choice in revealing information to Russia: "If you're in Putin's position, you have a guy with four laptops, with information that could be useful for his country.
"I can't imagine this guy showers with his laptops. There must be a point in time where the laptops get separated from the man. All they need is his key."