Sources told Fox News that Power tried to expose the identities of more than 260 Americans whose names surfaced in foreign intelligence documents, most in the final days of the Obama administration.
Previous U.N. ambassadors have made unmasking requests, but Fox News was told they number in the low double digits.
Power reportedly even sought information in the days leading up to President Donald Trump’s inauguration.
Some have alleged that Power, along with former National Security Adviser Susan Rice, misused the "unmasking" process, since it is intended for the intelligence community.
A spokesperson for Power had no comment on the number or timing of her requests, but her lawyer David Pressman claimed in a previous statement that she did nothing wrong.
"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," Pressman said. "Any insinuation that Ambassador Power was involved in leaking classified information is absolutely false."
Power has agreed to meet with the Senate and House intelligence committees on Capitol Hill next month as part of the Russia probe.
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