U.S. Special Counsel Robert Mueller on Friday handed in a confidential report on his investigation into Russia's role in the 2016 presidential election and any potential wrongdoing by U.S. President Donald Trump, setting off a clamor from lawmakers in both parties for the document's quick release.

Marking the end of his nearly two-year investigation that ensnared former Trump aides and Russian intelligence officers and cast a cloud over the Republican businessman's presidency, Mueller submitted the report to Attorney General William Barr, the Justice Department said.

It was not known if Mueller found criminal conduct by Trump or his campaign, beyond the charges already leveled against several aides. In all, Mueller brought charges against 34 people and three companies.

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Mueller, former FBI director, had been examining since May 2017 whether Trump's campaign conspired with Moscow to try to influence the election and whether the Republican president later unlawfully tried to obstruct his investigation.

Trump has denied collusion and obstruction. Russia has denied election interference. Trump has sought to discredit the investigation, calling it a "witch hunt" and accusing Mueller of conflicts of interest. 

But he said on Wednesday he does not mind if the public is allowed to see the report.

Mueller did not recommend any further indictments, a senior Justice Department official said, in a sign that there might be no more criminal charges against Trump associates arising from the investigation. 

But it was not immediately clear whether the special counsel had any sealed indictments that could later be disclosed.

The report was not immediately made public. Barr, the top U.S. law enforcement officer and a Trump appointee, will have to decide how much of it to disclose. 

Barr told lawmakers in a letter he may be able to provide the "principal conclusions" of Mueller's findings to Congress as soon as this weekend and added that he was "committed to as much transparency as possible."

Under regulations governing special counsel investigations, the attorney general must share an outline of 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.