Larry Page of Google and Mark Zuckerberg of Facebook have denied their companies have taken part in a United States government surveillance programme called PRISM.
The US government organised a huge dragnet of internet and phone data, with the FBI and National Security Agency tapping servers of nine internet companies - including Apple, Facebook, Microsoft, YouTube and Google.
All deny giving government agents access to servers.
Google said the government has no access, "not directly, or via a back door, or a so-called drop box".
The existence of the surveillance programme was reported by The Washington Post and The Guardian on Thursday.
President Barack Obama staunchly defended the PRISM system on Friday, saying the surveillance was legal.
In a related development, the BBC reports the British electronic eavesdropping agency GCHQ is to report to a parliamentary committee following accusations that it has gathered information from leading internet companies through the secret American surveillance programme.
The Intelligence and Security Committee Committee expects the report by Monday.
GCHQ said in a statement it operated to "a strict legal and policy framework".
