The US attorney general said Friday that he will release a redacted version by mid-April of the report on the two-year Russia election meddling probe, which had cast a cloud over Donald Trump's presidency.

Attorney General Bill Barr, in a letter to the chairmen of the House and Senate judiciary committees, said he was currently redacting sensitive material from the eagerly awaited report, which Trump has hailed as completely clearing him of allegations of collusion with Russia and obstruction of justice.

Special Counsel Robert Mueller, a former FBI director who headed the probe, was assisting with the task, he said.

"Our progress is such that I anticipate that we will be in a position to release the report by mid-April, if not sooner," Barr said.

The attorney general said the report was nearly 400 pages long excluding tables and appendices and "sets forth the Special Counsel's findings, his analysis and the reasons for his conclusions."

Barr, who released the "principal conclusions" of the report last week, has been under heavy pressure from Democrats to release the full report.

"I share your desire to ensure that Congress and the public have the opportunity to read the Special Counsel's report," the attorney general told the Senate and House judiciary committee chairmen.

"Everyone will soon be able to read it on their own," Barr said. "I do not believe it would be in the public's interest for me to attempt to summarise the full report or to release it in a serial or piecemeal fashion."

Representative Jerry Nadler, a Democrat who heads the House Judiciary Committee, responded to Barr's letter by saying he wanted the "full and complete Mueller report, without redactions" by April 2.

Redactions

Barr said the redactions underway included material "the intelligence community identifies as potentially compromising sensitive sources and methods."

Redactions also concern matters that the special counsel has referred to other Justice Department offices for investigation and information that would compromise the privacy of "peripheral third parties."

Barr said the report would not be submitted to the White House for review and Trump had deferred to him to deal with any parts over which he could invoke executive privilege.

Barr, citing the "principal conclusions" of the report last week, said the special counsel did not find that the Trump presidential campaign had conspired with the Russian government to win the 2016 election.

The "investigation did not establish that members of the Trump Campaign conspired or coordinated with the Russian government in its election interference activities," Barr quoted the report as saying.

Mueller also left the decision on whether Trump obstructed justice up to the attorney general, who determined that he had not "committed an obstruction-of-justice offence."

Regarding obstruction, Mueller stated that "while this report does not conclude that the President committed a crime, it also does not exonerate him."

Trump has welcomed the Mueller report as a "total exoneration" and blamed the media for pushing what he called the "Russian Collusion Delusion."

In his letter, Barr said he would be prepared to testify before the Senate and House judiciary committees on May 1 and May 2 respectively.