Australia’s role in what US President Donald Trump has dubbed “The Russia Hoax” could be further revealed when a long-awaited watchdog report is released.

US Department of Justice Inspector General Michael Horowitz will release a report on Monday (Tuesday AEDT) examining the FBI’s handling of the 2016 investigation into the Trump election campaign and potential links to Russia.

It was a May, 2016, bar meeting in London between then Australian high commissioner to the UK, Alexander Downer, and former Trump campaign foreign relations adviser, George Papadopoulos, that sparked the FBI investigation.

Mr Trump has claimed FBI officials were biased and working against him ahead of his November, 2016, election victory over Hillary Clinton.

The president predicted last month Mr Horowitz’s report would unearth “perhaps the biggest scandal in the history of our country”, but leaks to The Washington Post and other publications in recent days point to the opposite.

The watchdog found political bias did not influence the federal investigation, according to the reports.

Mr Horowitz also reportedly concluded the FBI had enough evidence to justify a foreign intelligence warrant to conduct surveillance of another former Trump campaign adviser, Carter Page.

Mr Trump and supporters are expected to latch on to Mr Horowitz’s findings that some FBI agents and lawyers involved in the probe acted in careless and unprofessional ways.

Mr Papadopoulous has alleged the FBI was part of an anti-Trump international espionage conspiracy involving the Australian intelligence, CIA, MI6,Turkish operatives, Mr Downer and a colourful bunch of characters including mysterious Maltese professor Joseph Mifsud.

Mr Trump has called for Australia’s role to be investigated and key Republicans have supported Mr Papadopolous’ claims.

The Australian government, Mr Downer, former director of US national intelligence James Clapper and other figures have rejected the claims.

Mr Downer said Mr Papadopoulos told him at the London bar meeting Russia had damaging material on Ms Clinton.

Mr Papadopoulos said he did not mention anything about Russian dirt on Mrs Clinton to Mr Downer.

Mr Horowitz’s report is being viewed by Trump supporters as only a prelude to another investigation led by US Attorney General William Barr and US Attorney for Connecticut John Durham.

Mr Trump called Australian Prime Minister Scott Morrison in September to ask for a point of contact between the Australian government and Mr Barr to help with the probe.

Donald Trump had been hoping a probe into the FBI would expose the biggest scandal in US history. Photo: Getty

Australian Ambassador to the US Joe Hockey confirmed Australia was cooperating.

In October Mr Hockey publicly rebuked senior US Republican Senator Lindsey Graham’s claim Mr Downer was “directed” in 2016 to contact Mr Papadopoulos and pass the Russian dirt information to the FBI.

Mr Horowitz’s report will be released at the same time the Democrat-controlled House Judiciary Committee continues impeachment hearings into Mr Trump’s dealings with Ukraine.

“I.G. report out tomorrow. That will be the big story!” Mr Trump tweeted on Sunday.

-AAP