Read: Mueller's letter to Barr

Democrats on the House Judiciary Committee on Wednesday released the letter special counsel Robert MuellerRobert (Bob) Swan MuellerTop Republican considered Mueller subpoena to box in Democrats Kamala Harris says her Justice Dept would have 'no choice' but to prosecute Trump for obstruction Dem committees win new powers to investigate Trump MORE sent to Attorney General William BarrWilliam Pelham BarrDemocratic lawmaker calls asylum, refugee programs 'crown jewel' of immigration system Trump says he won't watch Mueller testimony Cummings asks prosecutors about decision not to charge Trump in hush money probe 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.