Special Counsel Robert Mueller has handed in a keenly awaited report on his investigation into Russia’s role in the 2016 presidential election and any potential wrongdoing by US President Donald Trump, the Justice Department said.

Mr Mueller submitted the report to Attorney General William Barr, the top US law enforcement official, the department said.

The report was not immediately made public – Mr Barr will have to decide how much to disclose – and it was not known if Mr Mueller found criminal conduct by Mr Trump or his campaign beyond the charges already brought against several aides.

Mr Mueller, a former FBI director, had been examining since 2017 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 Trump has denied collusion and obstruction.

Russia has denied election interference.

The Russia investigation has cast a shadow over Mr Trump’s presidency and ensnared key figures including his former campaign chairman Paul Manafort, national security adviser Michael Flynn and personal lawyer Michael Cohen, who already have either been convicted or pleaded guilty to charges brought by Mr Mueller.

The big question now is whether the report contains allegations of wrongdoing by Mr Trump himself.

Mr Barr, a Trump appointee who took up his post in February, told lawmakers in a letter that he may be able to provide information to Congress on the report’s findings as soon as this weekend.

“The next steps are up to Attorney General Barr, and we look forward to the process taking its course. The White House has not received or been briefed on the Special Counsel’s report,” White House spokeswoman Sarah Sanders said.

Under the regulations governing special counsel investigations, the attorney general must share an outline of Mr Mueller’s report with Democratic and Republican leaders of the judiciary committees in Congress but it is largely up to him what to make public.

Lawmakers from both parties, including the Democratic chairman and the top Republican member of the House of Representatives Judiciary Committee, immediately called for prompt release of the Mueller report to key congressional committees and the public.

House Speaker Nancy Pelosi and Senate Democratic leader Chuck Schumer – the two top Democrats in Congress – said it was “imperative” that the full report be made public and that the White House play no role in determining what is released.

“The American people have a right to the truth. The watchword is transparency,” they said in a joint statement.

Mr Trump’s lawyers Jay Sekulow and Rudy Giuliani said they were pleased that Mr Mueller has delivered his report and that Mr Barr “will determine the appropriate next steps.”

Mr Trump has sought to discredit the investigation, calling it a “witch hunt” and accusing Mr Mueller of conflicts of interest.

US intelligence agencies have concluded that Moscow meddled in the election with a campaign of email hacking and online propaganda aimed at sowing discord in the United States, hurting Democratic candidate Hillary Clinton and helping Mr Trump.

-AAP