Edward Snowden has requested a meeting with human rights activists and lawyers at the airport in Moscow, where he has been stuck in transit for the last 3 weeks.

Those invited are reported to include representatives of Amnesty International and Human Rights Watch.

The fugitive whistleblower has been offered asylum by Venezuela, Bolivia and Nicaragua but has yet to accept any offer.

Snowden wrote a letter to a Human Rights official, reportedly accusing US officials of waging a campaign to stop him taking up offers of asylum.

Snowden's letter

"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.

"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 23rd and has been in limbo in Sheremetyevo airport's transit area despite 3 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.

Sheremetyevo airport, where Snowden has been stuck in transit for the last 3 weeks

Amnesty International

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 he said he wanted to discuss the "next steps forward in my situation" at 2pm Irish time. A top Moscow lawyer, Genri Reznik, said the meeting would be at 1.30pm Irish time and he expected Snowden wanted to explore the idea of getting asylum in Russia.

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.

Relations between President Obama and Russia's Vladamir Putin are poor

Microsoft

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, 9 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.