US President Donald Trump attacked the special investigator in the case of Russian intervention in the US presidential election, Robert Mueller, describing his investigations as false.

Trump, who was speaking at a conservatives' conference near Washington, said Muller took office by appointment and not by election by the American people.

He also attacked his opponents Democrats and described the patients, against the backdrop of plans to investigate the financial transactions, saying they are trying to get him out of the White House "nonsense."

"Unfortunately, you are putting people wrong in a number of locations and they are leaving people long in places where they should not be, and surprisingly they are trying to distract you from nonsense."

Muller is preparing to present a report to Justice Secretary William Bar, detailing his findings on the investigation into Russia's role in the 2016 presidential election and any connection to the Trump campaign.