(CNN) Former FBI Director James Comey has told the Senate intelligence committee he won't be constrained in discussing his conversations with President Donald Trump, Chairman Richard Burr said Monday.

Burr said he's spoken several times to Comey and he expects the former FBI director to talk in detail about his conversations with Trump when he testifies openly Thursday before the committee.

But Comey is expected to abstain from discussing the ongoing federal Russia investigation, a Senate intelligence committee source told CNN.

The broad boundaries, relayed by Comey to Burr and Vice Chairman Mark Warner last week, comes after Comey's discussions with Justice Department special counsel Robert Mueller, who is leading the agency's probe into the Trump campaign's ties to Russia.

Burr, a North Carolina Republican, said Monday he has not yet spoken to Mueller about Comey's expected testimony.

He added he does not think he needs to talk to Mueller before Comey's hearing but he does expect to.

JUST WATCHED Warner: hard to stop Comey from testifying Replay More Videos ... MUST WATCH Warner: hard to stop Comey from testifying 01:20

"As far as I'm concerned anything that would be off-limits would have to be expressed by the former director," Burr said of Mueller.

Burr and Warner, a Virginia Democrat, met Monday with acting FBI Director Andrew McCabe, and Burr said he raised the issue of Comey's memos about his dealings with Trump.

"I'd love to see the director's memos (before the hearing), but I don't think I will," Burr said.

The meeting with McCabe was not primarily about Comey's testimony, the senators said.

Burr also told CNN that former White House national security adviser Michael Flynn, a focus of the Russia probe, had turned over some of the documents to the Senate intelligence committee in response to a subpoena they issued last month.

A Flynn source told CNN they will submit "some documents soon based on their narrowed document requests after we objected."

Comey's memos are of particular interest to congressional investigators following reports last month that the then-FBI director wrote a memo following a meeting with Trump , detailing how the President allegedly asked Comey to end the investigation into Flynn. CNN has not viewed the memo but did have the memo described by sources familiar with the matter. Trump later denied Comey's description of the meeting

McCabe is one of several top administration officials testifying at a Wednesday intelligence committee hearing on a key National Security Agency surveillance law tool that expires at the end of the year.

Burr said he understood that the decision on the Comey memos was a "Justice Department determination."

The White House said Monday it would not invoke executive privilege to prevent Comey from testifying.