President Donald Trump said Tuesday that the FBI was "tainted" and used a "bogus" dossier to investigate his alleged links to Russia's supposed interference in the 2016 US presidential election.

"And they used this Crooked Hillary pile of garbage as the basis for going after the Trump Campaign!" Trump said in a Twitter post.

Trump was referring to a dossier, presumably harmful to his reputation, compiled last year by a private investigator and paid for, in part, by Democratic presidential candidate Hillary Clinton's campaign team.

In October, The Washington Post reported that the Clinton campaign and the Democratic Party had funded the investigation, which came to light after the November election and amid allegations about links between Trump and the Kremlin.

"WOW ... Dossier is bogus. Clinton Campaign, DNC funded Dossier. FBI CANNOT (after all of this time) VERIFY CLAIMS IN DOSSIER OF RUSSIA/TRUMP COLLUSION. FBI TAINTED," Trump tweeted.

Michael Caputo, a former Trump adviser, praised the president's tweets about the FBI, calling his posts an "insurance policy" against political bias in the federal law enforcement agency's investigations.

"The president's tweets are an insurance policy for the American people to make sure that its leading law enforcement organization remains unbiased," Caputo said on CNN's "New Day."

Tump has lashed out repeatedly at the FBI and US intelligence agencies.

In May, the president fired FBI Director James Comey, who was investigating alleged connections between Russia and the 2016 Trump campaign.