Special Counsel Robert Mueller complained in a letter to Attorney General William Barr that his four-page summary of Mueller's Russia report "did not fully capture the context, nature, and substance" of the investigation's conclusions, the Washington Post reported on Tuesday.

The Post said it reviewed a copy of Mueller's letter, which was written in late March after Barr released a summary on March 24 that said Mueller had found no evidence of collusion between President Donald Trump's campaign and Russia.

Barr also said in the summary that Mueller had not reached a conclusion on whether Trump obstructed justice. Barr said he and Deputy Attorney General Rod Rosenstein had found the evidence insufficient to support such a charge.

Barr's four-page summary was released more than three weeks before a redacted version of Mueller's 448-page report was released to the public on April 18.

Peter Carr, a spokesman for Mueller, declined to comment to Reuters.

"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," Mueller wrote, according to the Post.

"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," the Post quoted Mueller as writing.

(Cover: U.S. Attorney General William Barr departs after speaking at a news conference to discuss Special Counsel Robert Mueller's report on Russian interference in the 2016 U.S. presidential race, in Washington, DC, U.S., April 18, 2019. /Reuters Photo)