The main findings could be released as early as today of a 22-month investigation by Special Counsel Robert Mueller into Russia's role in the 2016 US election and any potential wrongdoing by US President Donald Trump.

US Attorney General William Barr, who received a report yesterday from Mr Mueller, told lawmakers in a letter that he may be able to inform them of Mr Mueller's "principal conclusions as soon as this weekend".

Under Department of Justice regulations, Mr Barr is empowered to decide how much to disclose publicly and he said in the letter that he is "committed to as much transparency as possible".

Mr Barr arrived at the department building in Washington this afternoon. He was reviewing the report, a Justice Department official said.

Democrats on the US House of Representatives Judiciary Committee scheduled a conference call for this evening to talk about next steps and messaging, congressional aides said.

Mr Trump, who is spending the weekend at his Mar-a-Lago resort in Florida, has not commented to reporters or taken to Twitter, one of his favourite ways of communicating, on the completion of the investigation that has cast a shadow over the Republican's two years in the White House.

Mr Trump had no public events scheduled today and was at his golf course in the morning. A large pro-Trump float pulled on a flatbed truck parked at the golf course about an hour after he arrived, adorned with American flags and "Trump 2020" signs. Political analysts expect the Mueller report to have an impact on how Democrats campaign to prevent Republican Trump being reelected.

The big question is whether the report contains allegations of wrongdoing by Mr Trump or exonerates him. Mr Mueller investigated whether Mr Trump's campaign conspired with Moscow to try to influence the election and whether the Republican president later unlawfully tried to obstruct his investigation.

Mr Mueller did not recommend any further indictments, a senior Justice Department official said, signaling there might be no more criminal charges against Mr Trump associates arising from the investigation.

Mr Mueller brought charges against 34 people and three companies over the course of his investigation, with prison sentences for some of Mr Trump's former aides.

Mr Trump's convicted former personal lawyer Michael Cohen implicated the president in his guilty plea on campaign finance violations in a separate prosecution brought by federal prosecutors in New York.

Mr Barr, who took office in February, was appointed by Mr Trump after the president fired his predecessor Jeff Sessions in November.

The White House has not received or been briefed on the report, spokeswoman Sarah Sanders said yesterday, adding that "we look forward to the process taking its course".

By handing over the long-awaited report to Mr Barr, Mr Mueller marked the end of his work, with his spokesman saying the 74-year-old former FBI director would conclude his service in the coming days.

Mr Trump has denied collusion and obstruction. Russia has denied election interference. Mr Trump has sought to discredit the investigation, calling it a "witch hunt" and accusing Mr Mueller of conflicts of interest. But he said on Wednesday he does not mind if the public is allowed to see the report.

Trump aides, including his former campaign chairman Paul Manafort, national security adviser Michael Flynn and personal lawyer Mr Cohen, have already either been convicted or pleaded guilty to charges brought by Mr Mueller.

None of those charges, however, directly related to the question of collusion between the campaign and Moscow. The US Justice Department has a policy that sitting presidents cannot face criminal charges.

House of Representatives Speaker Nancy Pelosi and Senate Democratic leader Chuck Schumer, the two top Democrats in Congress, said it was "imperative" the full report be made public, that Mr Barr not give Mr Trump and his team a "sneak preview" of the findings, and that the White House not be allowed to interfere in decisions about what parts are made public.

They said the investigation focused on questions that "go to the integrity of our democracy itself: whether foreign powers corruptly interfered in our elections, and whether unlawful means were used to hinder that investigation".