Democrats on the House Judiciary Committee are in negotiations with Special Counsel Robert Mueller for him to possibly testify before their panel, a source familiar with the talks told Fox News on Friday.

The source said that while committee Democrats have yet to set a date for a potential hearing, they have made progress and expect Mueller will agree to appear.

NADLER REQUESTS MUELLER TESTIFY BEFORE HOUSE JUDICIARY COMMITTEE 'AS SOON AS POSSIBLE'

A spokesperson for Mueller said he had no information and declined to comment. A spokesperson for committee Democrats did not immediately respond to Fox News’ request for comment.

The apparent negotiations have been shrouded in secrecy, but could point to another looming flashpoint in the battle between congressional Democrats and the Trump Justice Department over the final Mueller report on his investigation into Russia interference in the 2016 election.

The probe did not find evidence of Russia collusion with Trump associates but also did not reach a conclusion on the other component of the investigation -- whether President Trump obstructed justice. The entire debate surrounding the probe has since shifted to that subject, with Democrats accusing Attorney General Bill Barr of trying to shield the president by not including damaging details on that point in his initial summary of the report and by quickly determining there was no obstruction case to pursue.

In recent days, Democrats have renewed calls to hear from Mueller after a letter leaked showing he voiced concerns to Barr about the report summary following its release. Some Democrats have even charged that this contradicts testimony Barr delivered in April. Barr, for his part, boycotted a House Judiciary Committee hearing on Thursday over the terms of the session, though he testified for hours a day earlier on the Senate side. He also has refused requests for the unredacted Mueller report, though has offered access to a less-redacted version to certain lawmakers.

House Judiciary Committee Chairman Jerrold Nadler, D-N.Y., in a letter to Barr on Friday, threatened to begin contempt proceedings and “seek further legal recourse” should the attorney general and Justice Department continue their “baseless refusal to comply with a validly issued subpoena” for the full Mueller report.

Amid that tug-of-war, Democrats for weeks have seen Mueller as a potential key to unlock new details about the process, even as Trump and his allies declare it's time to move on.

It's unclear whether the notoriously tight-lipped Mueller would ultimately show up -- and on the Senate side, Judiciary Committee Chairman Lindsey Graham, R-S.C., has shown little interest in bringing Mueller in for a hearing, telling reporters, "It's over." He has since written to Mueller giving him the option of providing testimony if he wants to clear up any "misrepresentation" by Barr of their communications.

Last month, prior to Barr’s release of the full report, Nadler penned a letter to Mueller requesting he appear before the committee “as soon as possible” and “no later than May 23, 2019.”

“It is clear Congress and the American people must hear from Special Counsel Robert Mueller in person to better understand his findings,” Nadler said on April 18. “We are now requesting Mueller to appear before @HouseJudiciary as soon as possible.”

“I look forward to working with you on a mutually agreeable date,” Nadler wrote to Mueller last month.

House Speaker Nancy Pelosi, D-Calif., and Senate Minority Leader Chuck Schumer, D-N.Y., also called for Mueller to come before Congress.

“We believe the only way to begin restoring public trust in the handling of the Special Counsel’s investigation is for Special Counsel Mueller himself to provide public testimony in the House and Senate as soon as possible,” they wrote last month.

PELOSI SAYS BARR 'LIED TO CONGRESS' AND COMMITTED A CRIME, AS DOJ BLASTS 'RECKLESS' COMMENTS

While congressional Democrats have long sought Mueller’s testimony, a newly surfaced letter from the special counsel to Barr fueled their push.

The Washington Post first reported this week that Mueller contacted Barr, both in a letter and in a phone call on March 27, to express concerns about his initial report summary. Mueller pushed Barr to release the executive summaries written by the special counsel’s office.

However, according to both the Post and the Justice Department, Mueller made clear that he did not feel that Barr’s summary was inaccurate. Instead, Mueller told Barr that media coverage of the letter had “misinterpreted” the results of the probe concerning obstruction of justice.

Barr, testifying before the Senate Judiciary Committee this week, called Mueller’s comments “a bit snitty,” and said the situation was “mind-bendingly bizarre,” given that the report has been released to the public already.

Meanwhile, Pelosi this week accused Barr of lying to Congress and reportedly told colleagues in a closed-door meeting that he committed a crime.

“He lied to Congress. And if anybody else did that, it would be considered a crime,” she told reporters. “Nobody is above the law. Not the president of the United States. Not the attorney general.”

Pelosi’s public comments came after she, according to Politico, told Rep. Charlie Crist, D-Fla., during a private caucus meeting Thursday: “We saw [Barr] commit a crime when he answered your question.”

She was referring to an April 9 hearing, where Crist had asked whether Barr knew what prompted reports that prosecutors on the special counsel team were frustrated with his initial summary. Barr said he did not.

On Thursday, Pelosi was asked if Barr should go to jail for the alleged crime.

“There is a process involved here and as I said, I’ll say it again, the committee will have to come to how we will proceed,” Pelosi said.

Minutes later, the Justice Department blasted Pelosi for her assertions.

“Speaker Pelosi’s baseless attack on the Attorney General is reckless, irresponsible and false,” Justice Department spokeswoman Kerri Kupec told Fox News.

Fox News' Mike Emanuel contributed to this report.