A Justice Department official told former Special Counsel Robert Mueller that his upcoming testimony to House lawmakers "must remain within the boundaries" of the public, redacted version of his report, in a letter obtained by Fox News on Monday evening.

The letter, obtained by Fox News, signed by Associate Deputy Attorney General Bradley Weinsheimer, states: “Dear Mr. Mueller: I write in response to your July 10, 2019 letter concerning the testimonial subpoenas you received from the House Judiciary Committee (HJC) and House Permanent Select Committee on Intelligence (HPSCI).

“Your letter requests that the Department provide you with guidance concerning privilege or other legal bars applicable to potential testimony in connection with those subpoenas."

After stating the decision to testify is Mueller's to make, the letter continues: "But the Department agrees with your stated position that your testimony should be unnecessary under the circumstances. The Department generally does not permit prosecutors such as you to appear and testify before Congress regarding their investigative and prosecutorial activity.

READ THE FULL LETTER HERE

"In addition, the Department already has taken the extraordinary steps to make almost your entire report, as well as a substantial volume of your underlying investigative material, available to the committees.

"Should you testify, the Department understands that testimony regarding the work of the Special Counsel's Office will be governed by the terms you outlined on May 29 -- specifically, that the information you discuss during your testimony appears in, and does "not go beyond," the public version of your March 22, 2019 report to the Attorney General or your May 29 public statement."

It continued: "Finally, any testimony must remain within the boundaries of your public report because matters within the scope of your investigation were covered by the executive privilege, including information protected by law enforcement, deliberative process, attorney work product, and presidential communications privileges.

"These privileges would include discussion about the investigative steps or decisions, made during your investigation not otherwise described in the public version of your report. Consistent with standard practice, Department witnesses should decline to address potentially privileged matters, thus affording the Department the full opportunity at a later date to consider particular questions and possible accommodations that may fulfill the committees' legitimate need for information while protecting Executive Branch confidentiality interests."

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The letter comes after a deal was struck earlier this month for Mueller to give extended testimony as part of an agreement for him to appear before congressional lawmakers later this month, Democratic Party officials said at the time.

Mueller's highly anticipated appearance was pushed back at his request, Judiciary Chairman Jerrold Nadler, D-N.Y., and Intelligence Chairman Adam Schiff, D-Calif., said in a joint statement.

Mueller had been scheduled to testify on July 17 about the findings of his two-year Russia probe after he was subpoenaed by the panels last month.

The former special counsel's only public comments on the investigation came in May, when he did not clear Trump of wrongdoing and reaffirmed his reluctance to testify in front of Congress. He did not say whether Trump obstructed justice during his probe.

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“Charging the president with a crime was not an option we could consider,” he said at the time. Mueller's report did not assert that evidence showed Trump had, in fact, committed a crime.

Charges were brought against three businesses and 34 people, including former Trump aides, senior advisers, and Russian agents, although no Americans were indicted in connection with attempts to conspire with Russians to interfere with the 2016 presidential election. Mueller found no evidence the Trump team conspired with Russian actors, despite multiple outreach efforts aimed at involving the Trump campaign.

Mueller also told reporters any testimony he gave would not exceed what's contained in his report.

"There has been discussion about an appearance before Congress," Mueller said. "Any testimony from this office would not go beyond our report. It contains our findings and analysis, and the reasons for the decisions we made. We chose those words carefully, and the work speaks for itself. And the report is my testimony. I would not provide information beyond that which is already public in any appearance before Congress."