Read: Mueller's letter to Barr

Democrats on the House Judiciary Committee on Wednesday released the letter special counsel Robert MuellerRobert (Bob) Swan MuellerFox's Cavuto roasts Trump over criticism of network Mueller report fades from political conversation Trump calls for probe of Obama book deal MORE sent to Attorney General William BarrWilliam Pelham BarrSupreme Court comes to Trump's aid on immigration Words matter, except to Democrats, when it involves impeaching Trump Justice OIG completes probe on FBI surveillance of ex-Trump campaign aide MORE expressing frustration with Barr's summary of Mueller's Russia investigation.

"The summary letter the Department sent to Congress and released to the public late in the afternoon of March 24 did not fully capture the context, nature, and substance of this Office's work and conclusions," reads the letter signed by Mueller. "There is now public confusion about critical aspects of the results of our investigation. This threatens to undermine a central purpose for which the Department appointed the Special Counsel: to assure full public confidence in the outcome of the investigations."

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Mueller's office also provided documents it suggested the Department of Justice release to the public to supplement Barr's summary of the full report, which was released with redactions on April 18, several weeks after the summary.

"The Attorney General ultimately determined that it would not be productive to release the report in piecemeal fashion,” a Justice Department spokeswoman told The Hill of the documents provided by Mueller, saying Barr and Mueller discussed the letter in a "cordial" conversation by phone.

Barr is testifying before the Senate Judiciary Committee on Wednesday. Watch the live coverage here.

Read the full letter below.