James Comey 'looking forward' to testifying on Russia probe, Trump encounters: Richard Burr

The committee will hear from the former FBI director on Thursday.

"They've talked, and I understand the special counsel has not fenced him off in any way, shape or form on the items he intends to talk about," said Burr.

Trump told NBC News he fired Comey in part because of the “Russia thing,” which he called a “made-up story.”

The New York Times first reported the memo, which was confirmed to ABC News by a source close to Comey.

Burr also said his committee has begun receiving documents from Flynn, whose business interactions with Russian officials have come under scrutiny.

The House and Senate Intelligence Committee have both subpoenaed Flynn.

Comey’s appearance before the committee will be his first opportunity to discuss his encounters with Trump publicly since his surprise firing on May 9.

"We have seen these reports that are attributed to Comey, and the questions are going to be about if that's how it happened. No one has heard from him directly -- this will be the first time. That's what the whole hearing is going to be about," Sen. Marco Rubio, R-Florida, a member of the Senate Intelligence Committee, told ABC News in an interview.

ABC News’ Mary Bruce contributed to this report.