Hillary Clinton's presidential campaign and the Democratic National Committee helped pay for research that went into a dossier on Donald Trump's alleged campaign ties to Russia, according to a report in The Washington Post.

In April 2016, lawyer Marc Elias, working on behalf of the Clinton campaign and the DNC, retained Washington firm Fusion GPS to examine Mr Trump's Russia links, according to the report.

The payments continued until just days before the November 2016 election.

Even before that deal, Fusion GPS's research into Mr Trump was funded by a rival in the Republican presidential primary election.

That Republican's identity is not yet known.

Fusion GPS has asked that a federal judge block a House Intelligence Committee request to gain access to the company's bank records, saying it would violate its constitutional rights.

The 35-page political research dossier, prepared by former MI6 officer Christopher Steele, has become central to congressional probes into Russian interference in the 2016 US elections.

Mr Trump has branded the dossier - which contains salacious, and partially unconfirmed, political, financial and sexual allegations - as "fake news".

On Saturday, Mr Trump tweeted that the Justice Department and FBI "should immediately release who paid for it".

Two days earlier, he mused publicly on Twitter that Democrats may have funded the research.

"Workers of firm involved with the discredited and Fake Dossier take the 5th. Who paid for it, Russia, the FBI or the Dems (or all)?" the president wrote.

Protester heckles Trump, throws Russian flags

A protester threw small Russian flags at the US President yesterday and repeatedly shouted "Trump is treason" as he arrived on Capitol Hill for lunch with Republican politicians.

The man was just metres from Mr Trump and standing among a pool of reporters in a Senate hallway.

President Trump ignored the man, although he did give the thumbs-up sign as the red, white and blue flags of Russia fell at his feet, and kept walking along with Senate Majority leader Mitch McConnell.

"This president conspired with agents of the Russian government to steal the election," the protester shouted before being detained by Capitol police.

Mr Trump was at Congress to attend a weekly Republican luncheon and push his proposal for sweeping tax cuts.

The protester was identified as Ryan Clayton, leader of a group called Americans Take Action, which is pushing for President Trump to be impeached.

Mr Clayton was already known for having passed around Russian flags at a conference of conservative activists outside Washington.

Congressional panels and special prosecutor Robert Mueller are investigating whether the Trump campaign colluded with what US intelligence agencies have said were unmistakable Russian attempts to help Mr Trump defeat Ms Clinton in the November election.

The Russian Government has denied interfering in the election.