The Mueller report has found no evidence of conspiracy between President Donald Trump's campaign and Russia.
US President Donald Trump has declared he had been completely exonerated after his campaign was cleared of colluding with Russia in the 2016 election, in a major boost for his re-election hopes.
The long-awaited final report of Special Counsel Robert Mueller's probe into Moscow's election meddling concluded that no member or associate of the campaign conspired or coordinated with Russia in its plot to boost Mr Trump in the vote more than two years ago.
While not completely absolving the president, Attorney General Bill Barr's letter to Congress summarising the still-secret Mueller report cleared a dark cloud that had hung over Mr Trump's legitimacy since he took office in January 2017.
In its first reaction to details released from the politically explosive report into Mr Trump's Russia links, the White House said on Sunday that the president had been completely cleared.
"The special counsel did not find any collusion and did not find any obstruction," White Housespokeswoman Sarah Sanders said in a statement.
"The findings of the Department of Justice are a total and complete exoneration of the president of the United States."
Mr Trump later tweeted: "No Collusion, No Obstruction, Complete and Total EXONERATION. KEEP AMERICA GREAT!"
"It is a shame that our country had to go through this. To be honest, it is a shame our president had to go through this," he told reporters.
He called it an "illegal takedown that failed," and called for a new investigation of why the Russia investigation was launched.
US Vice President Mike Pence on Sunday said the report should be welcomed by all Americans.
"The special counsel has confirmed what President Trump said along; there was no collusion between the Trump campaign and Russia during the 2016 election," Pence said in a statement.
Rudy Giuliani, one of the president's lawyers, said on CNN that they viewed it as a "complete exoneration."
Mueller also declined to rule on whether evidence showed Mr Trump obstructed justice, according to a summary submitted to Congress by Attorney General Bill Barr.
"While this report does not conclude that the president committed a crime, it also does not exonerate him," Mr Barr quoted Mueller as writing in his report on the issue of possible obstruction of justice.
"The special counsel's investigation did not find that the Trump campaign or anyone associated with it conspired or coordinated with Russia in its efforts to influence the 2016 US Presidential Election," Mr Barr wrote in a letter to Congress.
Barr's summary said Mueller found no evidence that the Trump campaign coordinated with Russia, despite multiple offers from individuals associated with Russia.
House Judiciary Committee Chairman Jerry Nadler (D-N.Y.) expressed concerns over Barr's determination that Mr Trump did not obstruct justice.
He tweeted that "Special Counsel Mueller worked for 22 months to determine the extent to which President Trump obstructed justice.
Attorney General Barr took 2 days to tell the American people that while the President is not exonerated, there will be no action by DOJ."
That sentiment was echoed by House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer, who said in a statement, "Attorney General Barr's letter raises as many questions as it answers. The fact that Special Counsel Mueller's report does not exonerate the president on a charge as serious as obstruction of justice demonstrates how urgent it is that the full report and underlying documentation be made public without any further delay."
They said that Barr had a "record of bias" against Mueller's inquiry and was "not a neutral observer and is not in a position to make objective determinations about the report."
Top congressional Democrats said Sunday it was "urgent" the full report be publicly released.
"The fact that Special Counsel (Robert) Mueller's report does not exonerate the president on a charge as serious as obstruction of justice demonstrates how urgent it is that the full report and underlying documentation be made public without any further delay," House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer said in a joint statement.
The release of the summary is likely to ignite a new political fight in Washington as Democrats push for Barr to release the full report, and Mr Trump seizes on the findings as vindication of his near daily assertion that he was a victim of a "witch hunt" that has cast a long shadow over his presidency.
Mr Trump has always denied collaborating with Moscow or obstructing justice.
Russia says it did not interfere in the election, although US intelligence agencies concluded that it did.
Barr said the investigation also found insufficient evidence that Mr Trump had attempted to obstruct justice.
Many of his opponents accused him of obstructing the Russia probe when he fired former FBI director James Comey.
The Department of Justice announced on Friday that Mueller had ended his investigation after bringing charges against 34 people, including Russian agents and former key allies of the president, such as his campaign chairman Paul Manafort, former national security adviser Mike Flynn and his personal lawyer Michael Cohen.
None of those charges, however, directly related to whether Mr Trump's campaign worked with Moscow.
Earlier, Congress revealed it had received a letter from Mr Mueller's office.
"DOJ has just sent us a very brief letter about the Mueller report, which we will share shortly," Democratic Congressman Jerry Nadler said.
He also tweeted a portion of the letter allegedly sent today by the US Department of Justice.
“The Special Counsel states that ‘while this report does not conclude that the President committed a crime, it also does not exonerate him’,” the quote reads.
“The Department of Justice ‘determined not to make a traditional prosecutorial judgement’.”
Congressman Nadler is the chairman of the House Judiciary Committee and represents New York's 10th Congressional District.
The release comes after two days of bipartisan calls for the full Mueller report to be released publicly.
The investigation has been an daily distraction and irritant for Mr Trump for almost two years.
Opponents of the 45th president are hoping the report could lead to his eventual impeachment, if it proves damning.
Mr Trump remains at his resort in Palm Beach, Florida.
He’s previously condemned the Muller probe as a “witch hunt”.
“For two years we’ve gone through this nonsense. There’s no collusion with Russia,” he told Fox Business.
“And there’s no obstruction. They’ll say, ‘oh, well wait, there was no collusion, that was a hoax, but he obstructed in fighting against the hoax’.”
Earlier, Democrats pressed for full disclosure of special counsel Robert Mueller's report on the Trump-Russia investigation and vowing to use subpoena powers and other legal means if necessary to get it.
Key findings of the case:
US Attorney General Bill Barr released a summary Sunday of Special Counsel Robert Mueller's long-awaited report into allegations that Mr Trump's campaign colluded with Russia in the 2016 presidental election.
Here are the main findings of the two-year investigation the president regularly denounced as a witch hunt, before claiming vindication upon its completion.
Mueller found that there was conclusive evidence that Russia did interfere in the election, both through a coordinated campaign of disinformation and by hacking emails from Hillary Clinton's election team.
In a letter to lawmakers, Barr said that Mueller found that there had been "multiple offers from Russian-affiliated indivduals to assist the Trump campaign."
But quoting directly from Mueller's report, Barr said that the special counsel's investigation "did not establish that members of the Trump campaign conspired or coordinated with the Russian government in its election interference activities."
Many observers had predicted the biggest danger to Trump came from a possible accusation of obstruction of justice, particularly over his decision to sack the FBI director James Comey, who headed the investigation before Mueller.
But Barr said that the evidence outlined in Mueller's report "is not sufficient to establish that the President committed an obstruction-of-justice offence."
"In cataloguing the President's actions, many of which took place in public view, the report identifies no actions that, in our judgement, constitute obstructive conduct," Barr added in his letter.
But while Barr - who was appointed by Mr Trump - concluded that the president had not obstructed justice, he acknowledged that Mueller himself was inconclusive on the question of obstruction.
"The Special Counsel therefore did not draw a conclusion - one way or another - as to whether the examined conduct constituted obstruction," he said.
"The Special Counsel states that 'while this report does not condluce that the president committed a crime, it also does not exonerate him.'"
No more indictments
Mr Trump's former national security advisor Mike Flynn, his former personal lawyer Michael Cohen and his campaign chairman Paul Manafort are among the 34 individuals already indicted by Mueller but they will be the last, according to Barr.
"The report does not recommend any further indictments nor did the special counsel obtain any sealed indictments that have yet to be made public," Barr said in his letter to the heads of the Senate and House judiciary committees.