The National Security Agency plans to reveal details about terror plots it says were thwarted by surveillance, part of an effort to assuage concern about its secret online snooping.
In a rare move, the Agency (NSA) wants to declassify what its director says were dozens of foiled plots, which could help justify its sweeping operations in the eyes of sceptics worried about the vast amount of data being scooped up.
Senator Dianne Feinstein, chair of the powerful Senate Intelligence Committee, said NSA chief General Keith Alexander aimed to release the information on Monday but she is yet to hear from his office.
"I think what they want is to be certain that they're correct'' about the data they declassify, she told reporters.
Congressional officials announced that Alexander, who told a US Senate panel last week restoring the American people's trust in the NSA was a "sacred requirement,'' will appear before the House Intelligence Committee on Tuesday.
The hearing's title "How Disclosed NSA Programs Protect Americans, and Why Disclosure Aids Our Adversaries'' raises the prospect that his revelations would come during that testimony.
Feinstein said there were "a very small number of times'' the reasonable suspicion threshold had been invoked in order to access the trove of phone metadata.
House Intelligence Committee chairman Mike Rogers, who like Feinstein backs the programs, said Americans would become stronger supporters of the surveillance once they learn of its successes.
"If you can see just the number of cases where we've actually stopped a plot, I think Americans will come to a different conclusion than all the misleading rhetoric I've heard over the last few weeks,'' Rogers said on Sunday.
Republican former vice president Dick Cheney said he believed the defence contractor who leaked classified data about the programs, Edward Snowden, is "a traitor'' who committed crimes in revealing details about spy operations.