WASHINGTON (REUTERS) - US Attorney-General William Barr plans to make public a redacted copy of Special Counsel Robert Mueller's nearly 400-page investigative report into Russian interference in the 2016 election by mid-April, "if not sooner", he said in a letter to lawmakers on Friday (March 29).

"Everyone will soon be able to read it on their own," Barr wrote in the letter to the top Democrats and Republicans on the Senate and House Judiciary committees.

He said he is willing to appear before both committees to testify about Mueller's report on May 1 and 2.

Mueller completed his 22-month investigation into whether President Donald Trump's campaign colluded with Russia on March 22.

On Sunday, Barr sent a four-page letter to Congress that outlined Mueller's main findings. Barr told lawmakers that Mueller's investigation did not establish that members of the Trump campaign conspired with Russia in its election interference activities.

Mueller left unresolved the question of whether Trump obstructed justice during the investigation. Barr said that based on the evidence presented, he concluded it was not sufficient to charge the president with obstruction.

He said his letter on Sunday "was not, and did not purport to be an exhaustive recounting" of Mueller's investigation and said he believed the public should be allowed to read it and judge for themselves.

"I do not believe it would be in the public's interest for me to attempt to summarize the full report or release it in serial or piecemeal fashion," he wrote.

Lawmakers have since been clamoring for more details, with Democrats calling for a full release of the report and some lawmakers urging a deadline of April 2.

In a statement on Friday, House Judiciary Committee Chairman Jerrold Nadler said the April 2 deadline he imposed on the Justice Department "still stands" and he urged the release of a "full and complete" report without redactions.

The top Republican on the committee, Doug Collins, said on Twitter that Barr was "following his word" by pledging to release the report and chided Nadler for setting an arbitrary deadline.

Barr said in his letter on Friday that certain information must be redacted before the report is released, including secret grand jury information, intelligence sources and methods and information that by law cannot be public or might infringe on privacy.

Nadler rejected that notion, saying Barr must "work with us to request a court order to release any and all grand jury information to the House Judiciary Committee". The federal rules of criminal procedure make it a crime for government officials to publicly divulge sensitive grand jury materials such as transcripts, unless a federal judge signs off first.

Barr said on Friday that although Trump also has the right to assert executive privilege on some materials in the report to keep them from being made public, Trump has said publicly he intends to defer to Barr.

Because of that, Barr added, there were no plans for the Justice Department to submit the report to the White House for a privilege review.

Jay Sekulow, a personal lawyer for Trump, deferred to the White House for comment. The White House declined to comment.

Speaking at a news conference on Friday afternoon in Palm Beach, Florida, Trump said he "had a lot of confidence" in Barr.

At a rally on Thursday in Michigan, Trump had celebrated the end of the investigation and what he called "lies and smears and slander".