WASHINGTON - Washington is bracing for details from the long-awaited report of Special Counsel Robert Mueller on Russia's interference in the 2016 presidential election.

Attorney-General William Barr is due to brief Congressional leaders over the weekend on key findings from the report delivered on Friday.

There is initial triumphalism in conservative circles over the fact that, according to Department of Justice officials, no new indictments are forthcoming in the Russia probe.

Republicans flocked to declare President Donald Trump exonerated of suspicions of colluding with Russia to get elected. And attempting to impeach the President appears to be off the table.

But analysts are already calling the report only the end of the beginning, as it will almost certainly provide a blueprint for a slew of follow- up hearings and investigations of the President and his inner circle's policy decisions, financial interests, and personal relationships, by the Democratic-controlled House.

This would be on top of other ongoing investigations into the President and the family's Trump Organisation. On Friday, Reuters reported a source as saying Mr Trump's son-in-law and top aide Jared Kushner is cooperating with at least one of those investigations, by the House Judiciary Committee.

"The major difference is that the mystery before us has slightly changed form," Mr Benjamin Wittes, Senior Fellow in Governance Studies at the Brookings Institution, wrote in the Lawfare blog on Friday. "Before today, we asked what Mueller was going to do, what indictments he was going to bring, and what allegations he was going to make. Today, we ask a subtly different question: What is it that he has written? What allegations has he made?"

Mr Trump himself has long denied collusion, calling the investigation a witch hunt, even as the wide- ranging process produced indictments of 34 people and the conviction of five former Trump associates on various criminal charges ranging from money laundering to conspiracy against the US. Twenty-six of those individuals or entities indicted are Russian.

A clamour to make the Mueller report public erupted following its delivery on Friday to the Attorney-General, almost two years after the Special Counsel's investigation began. Mr Barr informed Congressional leaders in a letter that he may brief them on the report's "principal conclusions" over the weekend.

"I remain committed to as much transparency as possible, and I will keep you informed as to the status of my review," he said.

With only key findings expected to emerge, details may not be known until part or all of the report is released to the public.

In a joint statement, Democratic Party leader Nancy Pelosi and Senate Democratic leader Chuck Schumer urged Mr Barr to "make the full report public and provide its underlying documentation and findings to Congress" without giving Mr Trump or his attorneys a preview.

Democratic senator Amy Klobuchar, one of six Senate Democrats who have announced a run for the party's nomination in 2020, tweeted: "Attorney-General Barr must release the full report to the public. The American people deserve to know the facts."

And congressman Adam Schiff said House committees could subpoena the report and also Mr Mueller to testify on its revelations.

But Republican congressman Mark Meadows and a Trump ally tweeted: "The Mueller report delivery suggests no more indictments are coming from the Special Counsel. If that's true, it would mean we just completed two years of investigating 'Russian collusion' without ONE collusion related indictment. Not even one.

"Why? Because there was no collusion."

Republican congressman Steve Scalise, in a statement, said reports that no indictments have been recommended "confirm what we've known all along: There was never any collusion with Russia".

Analysts say not making the report public will only fuel speculation about what is being hidden. A February poll by the Washington Post found more than 80 per cent of Americans wanted the entire report made public.

Separate polls have found there is wide confidence in the fairness of the investigation. Mr Mueller is widely respected notwithstanding attacks on him by Mr Trump, who just said last week: "I had the greatest electoral victory… and now somebody's going to write a report, who never got a vote. So we'll see what the report says. Let's see if it's fair."