Moscow: Edward Snowden, a former US intelligence contractor who revealed the scope of the National Security Agency's (NSA) secret surveillance, has sworn allegiance to Russia.

He has been granted a Russian passport, according to TASS on Friday. According to Snowden's lawyer, Anatoly Kucherena, "Yes, he got [the passport] and he took the oath."

White House spokesman John Kirby informed reporters on Friday that "this is still a matter of a criminal investigation" and directed any questions about the Snowden report to the US Justice Department, which declined to comment. US officials have long demanded that Snowden be brought back to the country to face trial for espionage.

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Snowden, who left the United States after revealing top-secret documents exposing the widespread covert practices of the United States and its allies, was granted Russian citizenship in September by President Vladimir Putin.

The White House intentionally revoked my passport to keep me in Russia, and now I'm stuck there. They shot down the diplomatic plane of the President of Bolivia to prevent me from leaving, and they still hinder my freedom of movement today," Snowden, 39, wrote on Twitter Friday in reference to the 2013 situation.

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When Bolivia complained that its presidential jet carrying Evo Morales from Russia to Bolivia was forced to land in Austria on suspicion that Snowden was on board, Snowden was referring to an incident in July 2013.

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Snowden's supporters praise him as a contemporary dissident for revealing the scope of US espionage and alleged privacy violations. His detractors claim he is a traitor who has risked his life by revealing secret techniques used by Western spies to track militants and rival states.