WASHINGTON (BLOOMBERG) - US Attorney-General William Barr's letter summarising Special Counsel Robert Mueller's report is "a total and complete exoneration" of President Donald Trump, his press secretary said.

Mr Barr sent a letter to Congress on Sunday (March 24) reporting that Mr Mueller found no evidence that Mr Trump or his campaign aides conspired with Russian efforts to interfere in the 2016 US election.

Mr Barr also wrote that while Mr Mueller declined to make a judgment about whether Mr Trump committed obstruction of justice by interfering in investigations into the Russian meddling campaign, Mr Barr himself determined there wasn't sufficient evidence to charge the president.

"The special counsel did not find any collusion and did not find any obstruction," White House spokeswoman Sarah Sanders said in a statement, inaccurately describing Mr Mueller's findings.

"Attorney-General Barr and Deputy Attorney-General Rosenstein further determined there was no obstruction. The findings of the Department of Justice are a total and complete exoneration of the President of the United States."

Mr Trump's lawyer Rudy Giuliani said in a text message: "It's better than I expected."

Mr Trump's eldest son, Mr Donald Trump Jr, told Bloomberg News that Mr Barr's summary of Mr Mueller's report "proves what those of us with sane minds have known all along, there was ZERO collusion with Russia.

"Sadly, instead of apologising for needlessly destabilising the country in a transparent attempt to delegitimise the 2016 election, it's clear that the Collusion Truthers in the media and the Democrat Party are only going to double down on their sick and twisted conspiracy theories moving forward," Mr Trump Jr said.