Stephen Miller
Stephen Miller Reuters

White House senior policy adviser Stephen Miller has been interviewed as part of special counsel Robert Mueller's probe into ties between the Trump campaign and Russia, sources familiar with the investigation told CNN on Thursday.

The interview brings the special counsel investigation into President Donald Trump's inner circle in the White House. Miller is the highest-level aide still working at the White House known to have talked to investigators, the report noted.

Miller's role in the firing of FBI Director James Comey was among the topics discussed during the interview as part of the probe into possible obstruction of justice, according to one of the sources.

Special counsel investigators have also shown interest in talking to attendees of a March 2016 meeting where foreign policy adviser George Papadopoulos said that he could arrange a meeting between Trump and Russian President Vladimir Putin through his connections. Miller was also at the meeting, according to a source familiar with the meeting.

Papadopoulos was recently charged with lying to the FBI about Russian contacts he had during the campaign.

Mueller's team has also talked to key former aides, including former White House chief of staff Reince Preibus and former White House press secretary Sean Spicer. They have also interviewed National Security Council chief of staff Keith Kellogg.

The special counsel's office declined to comment. Miller did not respond to a request for comment.

Mueller was appointed in May by the Justice Department as special counsel to oversee the federal investigation into alleged Russian interference in the 2016 election.

His appointment was announced after Attorney General Jeff Sessions previously recused himself from any involvement in the Russia investigation due to his role as a prominent campaign adviser and surrogate.

Trump has argued that Mueller has hired "Hillary Clinton supporters" and people who worked for Clinton's 2016 White House bid to work on his investigation.

Indeed, reports emerged several weeks ago that a controversial dossier against Trump compiled ahead of the 2016 presidential election, which suggested then-candidate Trump colluded with the Russian government, was produced at the behest of the Clinton campaign and the Democratic National Committee.