(CNN) Susan Rice, who served as former President Barack Obama's national security adviser, quietly met behind closed doors Friday with Senate intelligence committee investigators probing Russian meddling in the elections, according to an official familiar with the matter.

Rice, one of three former Obama officials who met with the panel this week, has come under sharp scrutiny from some House Republicans because they believe she improperly "unmasked" -- or revealed the identities collected in intelligence gathering -- of Trump associates in US intelligence reports. She has vigorously denied any wrongdoing.

"Ambassador Rice met voluntarily with the Senate Select Committee on Intelligence today as part of the committee's bipartisan investigation into Russia's interference in the 2016 US presidential election," said Erin Pelton, a spokesperson for Rice, who also served as Obama's US ambassador to the United Nations. "Ambassador Rice appreciates the Committee's efforts to examine Russia's efforts to interfere, which violated one of the core foundations of American democracy."

Rice's appearance Friday marks the latest high-profile witness to privately meet with the panel ahead of the Senate's upcoming summer recess, with investigators meeting with former Obama chief of staff Denis McDonough and James Clapper, who was Obama's former director of national intelligence. And on Monday, Senate staff will interview Jared Kushner, the President's son-in-law and senior adviser, whose meetings with Russian officials have prompted serious questions from investigators.

Senate intelligence committee Chairman Richard Burr, a North Carolina Republican, told CNN this week that Obama and Trump officials both are on the witness list.

"Well I think we're interested in any folks that were in the last administration that had some hand in what we did or did not do in response to Russian meddling in our elections," Burr said in an interview. "I won't get into when they're coming or what the extent of the list is, but I think it's safe to say that we've had everybody that was involved in decision-making at the last administration on our list, and they're periodically coming. Some have been in. Some still have yet to come in."

Burr did not raise concerns about allegations that Rice improperly unmasked any US individuals, an issue first raised by House intelligence committee Chairman Devin Nunes.

"The unmasking thing was all created by Devin Nunes, and I'll wait to go through our full evaluation to see if there was anything improper that happened," Burr said. "But clearly there were individuals unmasked. Some of that became public which it's not supposed to, and our business is to understand that, and explain it."