White House senior adviser Stephen Miller Stephen MillerTrump confirms another White House staffer tested positive for COVID-19 Biden pick creates furor, underscoring bitterness over Obama immigration policy Ambassador to France says Trump never disparaged war dead MORE has been interviewed as part of special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE’s ongoing investigation into Russian influence over the 2016 election, CNN reported Thursday.

Miller is the highest-ranking current member of the Trump administration to be interviewed in Mueller’s investigation, signaling the probe is closing in on the White House.

Miller's role in the firing of former FBI Director James Comey was among the topics discussed during the interview, according to CNN.

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The special counsel's office did not immediately respond to a request for comment from The Hill.

Miller, 32, has played a key role in a number of White House policies, including the travel ban and rescinding the Deferred Action for Childhood Arrivals program that provided permits and deportation deferrals for young immigrants brought illegally to the U.S. as children.

Mueller has already filed charges against former Trump campaign members, including former campaign chairman Paul Manafort and his associate, Richard Gates.

George Papadopoulos, who worked on the campaign as a policy adviser, has pleaded guilty to lying to FBI investigators about his contact with Russian actors during the campaign.

Mueller has also interviewed former top Trump aides, including former White House chief of staff Reince Priebus and former White House press secretary Sean Spicer.

NBC News reported Sunday that Mueller has obtained enough evidence to bring charges against Trump’s former national security adviser Michael Flynn, who left the White House in February.