Samantha Power, the former U.S. ambassador to the United Nations, was 'unmasking' at such a rapid pace in the final months of the Obama administration that she averaged more than one request for every working day in 2016 – and even sought information in the days leading up to President Trump’s inauguration, multiple sources close to the matter told Fox News. 
Two sources, who were not authorized to speak on the record, said the requests to identify Americans whose names surfaced in foreign intelligence reporting, known as unmasking, exceeded 260 last year. One source indicated this occurred in the final days of the Obama White House.
The details emerged ahead of an expected appearance by Power next month on Capitol Hill. She is one of several Obama administration officials facing congressional scrutiny for their role in seeking the identities of Trump associates in intelligence reports – but the interest in her actions is particularly high.
OBAMA OFFICIAL MADE 'HUNDREDS OF UNMASKING REQUESTS,' GOP CHAIRMAN SAYS
In a July 27 letter to Director of National Intelligence Dan Coats, House Intelligence Committee Chairman Devin Nunes, R-Calif., said the committee had learned "that one official, whose position had no apparent intelligence-related function, made hundreds of unmasking requests during the final year of the Obama Administration."
The "official" is widely reported to be Power.
During a public congressional hearing earlier this year, Republican Rep. Trey Gowdy of South Carolina pressed former CIA director John Brennan on unmasking, without mentioning Power by name.
Gowdy: Do you recall any U.S. ambassadors asking that names be unmasked?
Brennan: I don't know. Maybe it's ringing a vague bell but I'm not -- I could not answer with any confidence.
Gowdy continued, asking: On either January 19 or up till noon on January 20, did you make any unmasking requests?
Brennan: I do not believe I did.
Gowdy: So you did not make any requests on the last day that you were employed?
Brennan: No, I was not in the agency on the last day I was employed.
Brennan later corrected the record, confirming he was at CIA headquarters on January 20. "I went there to collect some final personal materials as well as to pay my last respects to a memorial wall. But I was there for a brief period of time and just to take care of some final -- final things that were important to me," Brennan said.
Three of the nation's intelligence agencies received subpoenas in May explicitly naming three top Obama administration officials: Former national security adviser Susan Rice, Brennan and Power. Records were requested for Ben Rhodes, then-President Barack Obama's adviser, but the documents were not the subject of a subpoena.
A spokesperson for Power had no comment on the number or timing of her requests. But in a previous statement, her lawyer David Pressman emphasized that, "While serving as our Permanent Representative to the United Nations, Ambassador Power was also a member of the National Security Council responsible for advising the President on the full-range of threats confronting the United States. Any insinuation that Ambassador Power was involved in leaking classified information is absolutely false."
During congressional testimony since the unmasking controversy began, National Security Agency Director Adm. Mike Rogers has explained that unmasking is handled by the intelligence community in an independent review.
"We [the NSA] apply two criteria in response to their request: number one, you must make the request in writing. Number two, the request must be made on the basis of your official duties, not the fact that you just find this report really interesting and you're just curious,” he said in June. “It has to tie to your job and finally, I said two but there's a third criteria, and is the basis of the request must be that you need this identity to understand the intelligence you're reading."
Previous U.N. ambassadors have made unmasking requests, but Fox News was told they number in the low double digits.
Power has agreed to meet with the Senate and House intelligence committees as part of the Russia probe. She is expected before the House committee in a private, classified session in October.
Bret Baier is the Chief Political Anchor of Fox News Channel, and the Anchor & Executive Editor of "Special Report with Bret Baier.”  His book, "Three Days in January: Dwight Eisenhower’s Final Mission," (William Morrow) is on sale now.  
Catherine Herridge is an award-winning Chief Intelligence correspondent for FOX News Channel (FNC) based in Washington, D.C. She covers intelligence, the Justice Department and the Department of Homeland Security. Herridge joined FNC in 1996 as a London-based correspondent.