Special Counsel Robert Mueller has submitted his long-awaited report on alleged collusion between Russia and President Donald Trump's 2016 campaign.

A justice department official said Mr. Mueller's report did not recommend any further indictments.

The special counsel has already charged six former Trump aides and dozens of Russians.

The Attorney General William Barr will now summarise the report and decide how much to share with Congress.

Mr. Barr told congressional leaders in a letter that he anticipated being able to inform them of the report's key findings over the weekend.

The report is intended to explain any prosecutorial decisions the special counsel has made in the 22 months since his appointment by deputy US Attorney General Rod Rosenstein.

Mr. Trump and other Republicans have repeatedly condemned the probe as a "witch hunt".

In his letter to Congress' judiciary committee leaders - Senators Lindsey Graham and Dianne Feinstein and Congressmen Jerrold Nadler and Doug Collins - Mr. Barr confirmed there were no instances during the investigation where the Department of Justice had interfered with Mr. Mueller's work.

The attorney general said he will now consult with Deputy Attorney General Rosenstein - who managed the inquiry prior to Mr. Barr's appointment - and Mr. Mueller "to determine what other information from the report can be released to Congress and the public".

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

Over the past 22 months, the special counsel has revealed how Russian agents and operatives allegedly obtained information about US elections to initiate a campaign to influence Americans, fund political activities in the US and hack emails of top Democrats to undermine Hillary Clinton's campaign.