Neither meeting was revealed until Tuesday.

Justice Department spokeswoman Sarah Isgur Flores confirmed the Sessions meeting, which was also first reported by The New York Times. She declined to say if the attorney general turned over any documents or communications to Mueller's office.

Trump 'not at all concerned' about Sessions

The White House said it is cooperating with Mueller's investigation. White House special counsel Ty Cobb declined to comment when asked about the Sessions meeting, and the White House did not immediately return a request for comment about the Comey interview.

Trump told reporters Tuesday afternoon that he wasn't worried about what Sessions told Mueller's team.

"No, I'm not at all concerned," Trump said in the Oval Office. He added that he and Sessions did not discuss the conversation when the attorney general visited the White House on Monday.

According to CNN research , Sessions is the 15th member of the Trump administration, including former and current officials, who are known to have been interviewed in the Russia investigation that is currently led by Mueller and was previously led by Comey.

Last week, two people familiar with the process told CNN former White House chief strategist Steve Bannon has struck a deal with Mueller's team and will be interviewed by prosecutors instead of testifying before a grand jury. The sources did not say when the interview will take place or if the subpoena would be withdrawn.

Sessions announced he would recuse himself from all matters relating to the Russia investigation in early March 2017. Politicians, including Republicans, praised the decision at the time, but Trump has publicly rebuked his attorney general and said he wished Sessions had not recused himself.

Sessions' recusal left Justice Department oversight of the probe to Deputy Attorney General Rod Rosenstein, who appointed Mueller to be special counsel after Trump fired Comey in May 2017.

Earlier this month, the Times reported that Mueller is aware of an unsuccessful attempt by Trump to lobby Sessions to not recuse himself from the Justice Department's Russia probe.

Comey vs. Trump

Trump has railed against Comey since he fired the former FBI chief in May 2017.

It became public shortly after Comey's ouster that he had kept contemporaneous memos on conversations where he wrote that Trump asked him to let go of an investigation into former national security adviser Michael Flynn.

CNN reported in May that Mueller had been briefed on the contents of some of Comey's memos.

Comey, while still FBI chief, confirmed the existence of the Justice Department's Russia investigation, and in testimony for a June hearing after his firing, Comey affirmed his claim that Trump sought to influence ongoing investigations.

During that June hearing, Comey said he believed he was fired "because of the Russia investigation."

"I was fired in some way to change, or the endeavor was to change, the way the Russia investigation was being conducted," Comey said.