A top House Democrat said Friday it is too early to consider an immunity deal for former National Security Adviser Mike Flynn in exchange for testimony on alleged connections between Russia and the Trump campaign -- as the White House openly encouraged Flynn to testify.

Flynn’s attorney had said Thursday that the retired general is in discussions with the House and Senate intelligence committees, indicating he wants immunity from "unfair prosecution" in exchange for talking.

Rep. Adam Schiff, D-Calif., top Democrat on the House intelligence panel, on Friday called the idea a “grave and momentous step,” and one that apparently cannot be considered quite yet.

"[A]s with any investigation -- and particularly one that grows in severity and magnitude by the day -- there is still much work and many more witnesses and documents to obtain before any immunity request from any witness can be considered,” he said. He added that the committee will discuss it with Senate colleagues and the Justice Department.

That was after President Trump said on Twitter that Flynn was right to seek immunity, tweeting that he was being targeted by a “witch hunt” of “historic proportion.”

"He should go up there and he should testify," White House Press Secretary Sean Spicer said at Friday's press briefing.

Attorney Robert Kelner also said Thursday that Flynn is operating in a “highly politicized, witch hunt environment.” He said Flynn “certainly has a story to tell, and he very much wants to tell it, should the circumstances permit.”

Congress generally is skeptical toward granting immunity to committee witnesses and often defers to the Justice Department if there is a potential for criminal prosecution. Committees can grant an immunity order, which normally requires a two-thirds vote after prior approval from the Justice Department.

Congressional committees have obtained some 300 immunity orders since Congress passed an immunity law in 1970, many of which were tied to a probe into the assassinations of President John F. Kennedy and Martin Luther King Jr.

During the Obama administration, former IRS official Lois Lerner sought immunity for her testimony to Congress, which was investigating how she and other officials scrutinized conservative groups. The committee declined to grant her request. She was still called to testify at a hearing, where she repeatedly invoked her Fifth Amendment right to protect herself against self-incrimination.

Flynn’s connections to Russia are being looked at by the FBI and form part of the Russia probe by the House and Senate intelligence committees.

Flynn resigned in February after media reports showed he misled Vice President Mike Pence about a conversation he had with the Russian ambassador during the transition period.

Trump and allied Republicans, though, say a bigger problem is the leaking of sensitive information and potential surveillance of Trump associates under the prior administration. House Intelligence Committee Chairman Devin Nunes says he’s learned some Trump team communications were incidentally collected during the transition – information he apparently found out with help from White House aides, a detail that has only fueled Democratic complaints.

Fox News’ Chad Pergram and The Associated Press contributed to this report.