An Obama official made “hundreds of unmasking requests” during the final year of the previous administration, according to a letter from a top Republican who raised new concerns that officials sought the identities of Trump associates in intelligence reports for “improper purposes.”

“Unmasking” refers to the formal request to identify Americans in an intelligence document.

CLICK HERE TO READ THE LETTER

House Intelligence Committee Chairman Devin Nunes, R-Calif., has questioned whether Obama officials improperly sought the names of Trump transition members in this way – and, in the letter obtained by Fox News, Nunes provided new details about what his investigators have found.

“[T]his Committee has learned that one official, whose position has no apparent intelligence-related function, made hundreds of unmasking requests during the final year of the Obama Administration,” he wrote to Director of National Intelligence Dan Coats.

Only one request, Nunes wrote, “offered a justification that was not boilerplate and articulated why” the identity was needed for official duties.

Three of the nation’s intelligence agencies received subpoenas in May explicitly naming three top Obama administration officials: Former CIA director John Brennan, former national security adviser Susan Rice, and former U.N. ambassador Samantha Power.

Nunes’ letter appears to make reference to Power as the official who made “hundreds” of requests.

However, David Pressman, counsel to Power and partner at Boies Schiller Flexner LLP, stressed Power’s responsibilities in her capacity as a member of the National Security Council and denied she leaked anything classified.

"Long before receiving an invitation to engage the Congressional committees, Ambassador Power was unambiguous about her support of bipartisan efforts to determine the full extent of this threat to our national security," he said in a statement. "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."

The Nunes letter also said he plans to introduce a bill requiring “individual, fact-based justifications” for such unmasking requests. “Cabinet members and other senior political leaders cannot be permitted to continue to seek access to U.S. person information within disseminated intelligence reports without documenting a specific, fact-based requirement for the information,” he wrote.

Explaining his concerns, Nunes said in the letter that “Obama-era officials sought the identities of Trump transition officials within intelligence reports” without offering any “meaningful explanation” as to why they needed or how they would use the information.

The committee, Nunes wrote, “is left with the impression that these officials may have used this information for improper purposes, including the possibility of leaking.” He noted that some of the requests were “followed by anonymous leaks of those names to the media.”

Intelligence agencies typically are required to conceal the identities of Americans picked up or mentioned in surveillance of foreigners in the U.S. Formal requests need to be made to release those names.

Several Obama administration officials met privately last week with staffers on Capitol Hill. Among them, Rice met Friday with Senate Intelligence Committee staffers. Power also has agreed to testify before the House Intelligence Committee.

Rice told MSNBC in April that allegations Obama administration officials used such intelligence for political purposes is “false.”

Media reports earlier this year revealed, among other conversations, those between then-national security adviser Michael Flynn and then-Russian ambassador to the U.S. Sergey Kislyak. Reports of those conversations led to Flynn's resignation in February.

Nunes is continuing to pursue the unmasking issue, though he has stepped aside from leading the Russia investigation – and is facing an ethics inquiry over whether he improperly revealed classified information. Nunes disputes the charge. Fox News asked a spokesman for Brennan for comment but there was no immediate response.

Fox News’ Catherine Herridge contributed to this report.