Snowden has very sensitive "blueprints" detailing how the National Security Agency operates and that would have exposed American intelligence like never before.
The details with Snowden if released, could equip people to evade NSA surveillance or misuse the setup details by duplicating it.
Instruction manual on NSA
The former NSA systems analyst has thousands of documents that constitute a kind of instruction manual for how the NSA is built.
This was revealed by Glenn Greenwald, who broke Snowden story on The Guradian newspaper.
"Snowden has enough information to cause more damage to the US government in a minute alone than anyone else has ever had in the history of the United States," Greenwald told Argentina's La Nacion paper in an interview published on Saturday.
Not to be made public
Greenwald also told a news agency that Snowden has insisted the information from those documents not be made public.
Snowden emerged from weeks of hiding in a Moscow airport on Friday, and said he was willing to meet President Vladimir Putin's condition that he stop leaking US secrets if it means Russia would give him asylum until he can move on to Latin America.
Snowden also said he did not want to harm the United States.
(with agencies inputs)