In the letter -- posted on the Facebook page of Lokshina, the Russian Human Rights Watch staffer -- the writer praised the "brave countries" that have offered him support, in the face of what he described as "an unlawful campaign by officials in the U.S. Government to deny my right to seek and enjoy this asylum."
In her Facebook post, Lokshina said she received the e-mailed invitation close to 5 p.m. Thursday and acknowledged that she did not know beforehand if it was real.
A large group of Russian and international journalists gathered at the airport in anticipation of the meeting.
Latin American asylum offers
Since his arrival in Moscow, Snowden -- who faces espionage charges in the United States -- has requested asylum in dozens of countries, sparking a surge in speculation about his next steps.
Snowden has admitted releasing classified documents about U.S. surveillance programs to the media and argues that he did so to expose serious violations of the U.S. Constitution.
He is slammed as a traitor by critics and hailed as a hero by his supporters.
WikiLeaks said in a Twitter post Wednesday that Snowden's "flight of liberty" campaign was starting, promising further details.
But details about where Snowden is going -- and how he'll get there -- have remained hard to come by.
U.S. officials told Chinese officials in Washington this week that they're disappointed with the way China and Hong Kong handled the Snowden case, saying their actions undermined trust. China said that Hong Kong authorities acted in accordance with the law.