Intelligence services whistleblower Edward Snowden has reportedly accused US officials of waging a campaign to stop him taking up offers of asylum.
The claim was made in a letter sent to a Human Rights Watch official, ahead of a meeting with human rights groups at the Moscow airport where he has been holed up for weeks.
The letter said: "I have been extremely fortunate to enjoy and accept many offers of support and asylum from brave countries around the world. These nations have my gratitude.
"Unfortunately, in recent weeks we have witnessed an unlawful campaign by officials in the US government to deny my right to seek and enjoy this asylum under Article 14 of the Universal Declaration of Human Rights.
Protesters have shown their support for Snowden "The scale of threatening behaviour is without precedent: never before in history have states conspired to force to the ground a sovereign president's plane to effect a search for a political refugee."
That remark appears to refer to how Austrian authorities last week searched the Bolivian president's plane when it was diverted to Vienna because the US suspected Snowden was on board.
The letter continues: "This dangerous escalation represents a threat not just to the dignity of Latin America or my own personal security, but to the basic right shared by every living person to live free from persecution."
Snowden is wanted by the US on espionage charges over a series of leaks about spying programmes, with his most recent claims involving collaboration between Microsoft and American intelligence services.
He fled to Moscow from Hong Kong on June 23 and has been in limbo in Sheremetyevo airport's transit area despite three countries - Venezuela, Nicaragua and Bolivia - saying they would be willing to grant him asylum.
It is unclear whether Snowden could fly from Moscow to any of those countries without passing through the airspace of the US or its allies.
The head of Amnesty International in Russia, Sergei Nikitin, confirmed he had been invited to meet the former National Security Agency contractor there and said he planned to attend.
In the letter to Human Rights Watch, Snowden said he wanted to discuss the "next steps forward in my situation" at 2pm UK time.
A top Moscow lawyer, Genri Reznik, said the meeting would be at 1.30pm UK time and that he expected Snowden wanted to explore the idea of getting asylum in Russia.
Snowden's latest evidence concerns the NSA spying on Skype video calls Snowden is seeking to avoid extradition after divulging embarrassing evidence about the activities of US spies, as well as the British eavesdropping agency GCHQ, to newspapers including The Guardian.
The latest files said Microsoft helped America's National Security Agency (NSA) to circumvent encryption so it could view web chats on the Outlook.com portal, which is replacing Hotmail.
Evidence seen by the paper said Microsoft also worked to give the NSA easier access to its cloud storage service SkyDrive, which has more than 250 million users. And by July 2012, nine months after Microsoft bought Skype, the Prism intelligence programme was collecting triple the amount of Skype video calls.
Major tech firms in Silicon Valley have been calling on the Obama administration to let them reveal more about their co-operation with the NSA, to alleviate customers' privacy concerns.
Microsoft told the paper it only provides information about users when demanded to do so by the government.
Snowden's files revealed the NSA claimed to have access to the servers of web firms including Apple, Google, Facebook and Yahoo, while GCHQ scans vast amounts of internet traffic through a system of fibre optic cables.
The US on Thursday told China it was "disappointed" that Snowden was not handed over before he had a chance to leave Hong Kong. He had fled to the Chinese territory after he began to leak documents.
President Barack Obama expressed his "concern" as he met with Chinese officials in Washington, a month after he and his Chinese counterpart Xi Jinping had agreed to co-operate more on "difficult issues".
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