Barr ends his letter to Congress by saying he will release more from the full report, but that some of the material is subject to grand jury investigation restrictions.

"Given these restrictions, the schedule for processing the report depends in part on how quickly the Department can identify the [grand jury] material that by law cannot be made public.

"I have requested the assistance of the Special Counsel in identifying all information contained in the report as quickly as possible.

"Separately, I also must identify any information that could impact other ongoing matters, including those that the Special Counsel has referred to other offices.

"As soon as that process is complete, I will be in a position to move forward expeditiously in determining what can be released in light of applicable law, regulations and Departmental policies."

The second part of the report addresses the issue of obstruction of justice. Barr’s summary says the Special Counsel report "ultimately determined not to make a traditional prosecutorial judgment".

It goes on: "The Special Counsel therefore did not draw a conclusion – one way or the other – as to whether the examined conduct constituted obstruction."

The letter then quotes directly from Mueller: "While this report does not conclude that the president committed a crime, it also does not exonerate him."

Image source, AFP/Getty Images

As US attorney general overseeing the politically independent US Department of Justice, William Barr is the top law enforcement officer in the nation.

He was confirmed for the post in February by the Senate after a vote that largely fell along party lines.

During his confirmation hearing Democrats were angered by his previous criticism of the Russia inquiry and his past arguments that appeared to support Trump’s public positions.

Barr, who also served as attorney general from 1991-93, previously argued in a memo that Trump was within his rights to fire FBI director James Comey and that Hillary Clinton’s actions merited an inquiry more than any Trump-Russia collusion.

Democrats slammed the memo as a "job application" for the role that he now finds himself in.

According to Barr's letter, Mueller's team found two main Russian efforts to influence the 2016 US election, both by Russian groups and the Russian government:

1. "Attempts by a Russian organisation, the Internet Research Agency, to conduct disinformation and social media operations in the United States designed to sow social discord, eventually with the aim of interfering with the election."
2. "Russian government's efforts to conduct computer hacking operations designed to gather and disseminate information to influence the election...Russian government actors successfully hacked into computers and obtained emails from persons affiliated with the Clinton campaign and Democratic Party organisations and publicly disseminated those materials through various intermediaries, including WikiLeaks."

Democrats have been calling for transparency since the inquiry began.

Legally, the attorney general is under no obligation to release the report publicly, and his copy to Congress could contain redactions, but during his confirmation hearings before senators Mr Barr vowed to release as much as he could.

A number of senior Democrats, including presidential hopefuls Beto O'Rourke, Bernie Sanders, Cory Booker, Amy Klobuchar, Kirsten Gillibrand, and Julian Castro, have called for the full release of the report.

Congressman Nadler echoed those calls on Sunday.

Here's everyone who has been charged during the course of the Mueller inquiry into alleged Russian meddling. And, as there are no more indictments to come, this could be the final list.

The uproar in Washington began after President Trump fired FBI Director James Comey in May 2017.

Two days later Trump told NBC News the dismissal was because of "this Russia thing with Trump and Russia is a made-up story".

Deputy Attorney General Rod Rosenstein then appointed Robert Mueller to lead an investigation into suspected Russian meddling in the 2016 election.

The decision fell to the deputy after Attorney General Jeff Sessions earlier recused himself over conversations with the Russian ambassador to the US while Sessions was working for the Trump campaign.

Within a month, the Mueller investigation expanded to include possible obstruction of justice by Trump, his campaign team, and members of his inner circle and family.

Congressman Jerry Nadler, the Democratic Chair of the House of Representatives Judiciary Committee, emphasised that the attorney general did not rule out that Trump had obstructed justice.

"Barr says that the President may have acted to obstruct justice, but that for an obstruction conviction, 'the government would need to prove beyond a reasonable doubt that a person, acting with corrupt intent, engaged in obstructive conduct'."

Republican Doug Collins, ranking member of the House Judiciary Committee, said: "There is no constitutional crisis."

Republican Senator Lindsey Graham, Chairman of the Senate Judiciary Committee and a vocal Trump supporter, said it was a "good day for the rule of law" and a "great job by Mr Mueller and his team to thoroughly examine all things Russia".

Deputy Attorney General Rod Rosenstein and Barr have "concluded that the evidence developed during the Special Counsel's investigation 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 judgment, constitute obstructive conduct".

"The Special Counsel recognised that the evidence does not establish that the President was involved in an underlying crime related to Russian election interference".

On collusion the report specifically states: “[T]he investigation did not establish that members of the Trump Campaign conspired or coordinated with the Russian government in its election interference activities."

• 2,800 subpoenas
• 500 witnesses interviewed
• Nearly 500 search warrants
• 230+ orders for communication records
• 13 requests to foreign governments for evidence

Barr's letter notes that all of the indictments have been publicly disclosed and the report "does not recommend any further indictments".

Attorney general's letter to Congress: "The special counsel considered whether to evaluate the conduct under Department standards governing prosecution and declination decisions but ultimately determined not to make a traditional prosecutorial judgement."

It goes on: “The Special Counsel therefore did not draw a conclusion – one way or the other – as to whether the examined conduct constituted obstruction.

"Instead, for each of the relevant actions investigated, the report sets out evidence on both sides of the question and leaves unresolved what the Special Counsel views as 'difficult issues' of law and fact concerning whether the President's actions and intent could be viewed as obstruction.

"The Special Counsel states that 'while this report does not conclude that the President committed a crime, it also does not exonerate him'."

Key line from attorney general's letter: "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."

The four-page letter , externalis addressed to Judiciary Committee Senators Lindsey Graham, Dianne Feinstein and Congressmen Jerrold Nadler and Doug Collins.

It is a summary of the principal conclusions of Robert Mueller's investigation into alleged collusion between Russia and Donald Trump's campaign as well as possible obstruction of justice by the president.

It is not the full Mueller report, which remains in Attorney General Barr's hands.

Attorney General William Barr has submitted a four-page summary of the special counsel's report to Congress.