The 448-page, two-volume report prepared after 22 months of investigations by Mueller was sent on Thursday to Congress on CD-ROM disks and released online.

While it may have quelled allegations of Russian collusion, it dropped several hints that Trump tried to interfere with the investigations, which have the potential of developing into criminal charges of obstruction of justices.

The report said that it could neither confirm nor rule out "that no criminal conduct occurred" on the obstruction of justice allegations, explicitly acknowledging that Congress could have jurisdiction over the matter.

The report said that Trump had phoned then-White House lawyer Don McGahn and asked him to tell Deputy Attorney General Rod Rosenstein that Mueller was conflicted and should be removed. It added, however, that McGahn refused to do that.

Democrats vowed to pursue the obstructions allegations. House of Representatives Judicial Committee Chairman Jerry Nadler, a Democrat, said he would order Mueller himself to appear before his panel before May 23 to explain his findings. "It is clear Congress and the American people must hear from Special Counsel Robert Mueller in person to better understand his findings," he tweeted.

On the focus of the probe, the report said: "While the investigation identified numerous links between individuals with ties to the Russian government and individuals associated with the Trump Campaign, the evidence was not sufficient to support criminal charges".

While the report said "the evidence uncovered in the investigation did not establish that the President or those close to him were involved in the charged Russian computer-hacking or active-measure conspiracies, or that the President otherwise had an unlawful relationship with any Russian official", it tantalisingly added: "But the evidence does indicate that a thorough FBI (Federal Bureau of Investigation) investigation would uncover facts about the campaign and the President personally that the President could have understood to be crimes or that would give rise to personal and political concerns".

This seemed to be mainly about the business dealings Trump had in Russia.

The report sketched out the Russian meddling in the elections, which started in 2014, in great detail. It detailed Russian military intelligence agency GRU's hacking of e-mails of Democratic Party and it leaders that were leaked to WikiLeaks and sowed dissensions within the party.

It also said "the Internet Research Agency, a Russian company with close ties to the Russian government, to sow social discord among American voters through disinformation and social media operations".

Mueller's report said, "Although the investigation established that the Russian government perceived it would benefit from a Trump presidency and. worked to secure that outcome, and that the campaign expected it would benefit electorally from information stolen and released through Russian efforts, the investigation did not establish that members of the Trump Campaign conspired or coordinated with the Russian government in its election interference activities."

The report also gave an inside look at the Trump's inner circle gleaned from officials it interviewed with juicy tidbits like Trump exclaiming after the Mueller inquiry was established, "This is the end of my Presidency. I'm (expletive)".

It enumerated ten instances where Trump could have potentially interfered with the Mueller probe through intimidation in the media or attempts to end it or pressuring officials.

Before releasing the report, US Attorney General William Barr told reporters that "all Americans can and should be grateful to have confirmed" through Mueller's investigation that the Russian "schemes did not have the cooperation of President Trump or the Trump campaign -- or the knowing assistance of any other Americans for that matter".

He blacked out portions of the report because they relate to confidential intelligence matters, to testimony that is secret under the law or to innocent individuals or to ongoing investigations or court cases.

He said that he would show Congressional leaders the redacted parts of the report that he legally could.

Demanding the release of the report in full, Democratic Senator Kamala Harris tweeted: "Americans deserve the unvarnished truth".

"The American people deserve the truth, not a sanitised version of the Mueller Report approved by the Trump Admin", Speaker Nancy Pelosi tweeted from Ireland, where she is on a visit.

In his theatrical style, Trump reacted with tweet of a picture of him like a movie poster proclaiming, "No Collusion. No obstruction. For the haters and the radical left Democrats a Game over", and tweeted on Thursday morning his consistent position on the inquiry: "The Witch Hunt has been a total fraud on your President and the American people! It was brought to you by Dirty Cops, Crooked Hillary and the DNC (Democratic National Committee)".

Democrats assailed Barr for holding a news conference before releasing the report. Harris tweeted: "Barr is acting more like Trump's defense attorney than the nation's Attorney General. His press conference was a stunt, filled with political spin and propaganda."

During his news conference, Barr defended his controversial decision to not pursue obstruction of justice charges against Trump after Mueller had not come to a conclusion about it and had left it Barr to decide if a prosecution was warranted.

Barr said Mueller had looked into ten instances where there could have been interference by Trump to impede the investigation but he and Deputy Attorney General Rod Rosenstein concluded that there was not enough evidence to launch a prosecution.

Barr dismissed culpability of the Trump campaign in disseminating emails of the Democratic National Committee and Hillary Clinton that were hacked by Russians and proved embarrassing to the Democratic candidate's campaign.

He explained that "publication of these types of materials would not be criminal unless the publisher also participated in the underlying hacking conspiracy" and "the special counsel's report did not find that any person associated with the Trump campaign illegally participated in the dissemination of the materials".

This is a defence used by news media in publishing material hacked by others like WikiLeaks -- that they themselves did not break the law by hacking.