Donald Trump’s administration has threatened to use his executive privilege to block Democrats’ attempts to access the full, unredacted Mueller report.

If opposition politicians pushed ahead with a planned vote to hold William Barr in contempt of Congress, the Justice Department (DoJ) warned, the attorney general would be "compelled to request that the president invoke executive privilege with respect to the materials" Democrats want to see.

Mr Barr has been resisting a subpoena issued by the Democrats for the full document.

He released a redacted version to the public last month, and his department has rejected demands for an unredacted copy while allowing a handful of politicians to view a version of Robert Mueller‘s report with fewer elements removed.

The DoJ had been locked in negotiations with Democratic members of the House Judiciary Committee on Tuesday before handing down the executive privilege ultimatum in a letter from Mr Barr’s deputy, Stephen Boyd.

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Committee chairman Jerry Nadler dismissed the threat, saying in a statement that “this is, of course, not how executive privilege works”.

“The White House waived these privileges long ago, and the department seemed open to sharing these materials with us earlier today. The department’s legal arguments are without credibility, merit, or legal or factual basis,” he added.

The DoJ said on Monday that it had ”taken extraordinary steps to accommodate the House Judiciary Committee’s requests for information” regarding Mr Mueller’s report, but that Mr Nadler had not reciprocated. A spokeswoman noted that Democrats had refused to read the version with fewer redactions provided to Congress.

It was not immediately clear how a claim of executive privilege would work in relation to the special counsel’s probe. The power allows a president to keep information from the courts, Congress and the public to protect the confidentiality of the Oval Office decision-making process.

The DoJ’s threat came only hours after the White House moved to prevent Donald McGahn, a central witness for Mr Mueller and the administration’s former top lawyer, from giving certain documents to congressional investigators because Mr Trump may invoke privilege over them, the New York Times reported.

The contempt vote was due to take place on Wednesday.

Mr Nadler also said he expected the committee would hold Mr McGahn in contempt if he did not appear before it, “unless the White House secures a court order directing otherwise”.