US President Donald Trump asked Prime Minister Scott Morrison to investigate an Australian diplomat on a recent phone call, according to a report released by the New York Times.

Citing two American officials, the Times reports Mr Trump asked Mr Morrison to work with US Attorney General William Barr to gather information that would help discredit a long-running investigation into Russian interference in the 2016 election.

The report doesn't state who the target of the investigation is, but 9News understands it was former Foreign Minister and UK High Commissioner Alexander Downer.

Scott Morrison and Donald Trump held meetings in the US last month. (AAP)

Mr Downer's role in the Russian interference investigation followed a meeting with George Papadopoulos in 2016, when Mr Downer was serving as High Commissioner and Mr Papadopoulos was an adviser to Mr Trump's election campaign.

Over a night of drinking, Mr Papadopoulos revealed that Russia may have possessed damaging information on Democratic candidate Hillary Clinton.

Mr Downer says he reported the information to Australian officials in the following days.

Mr Papadopoulos has long blamed Mr Downer for beginning the investigation while also spouting conspiracy theories about "deep state" involvement.

The investigation resulted in dozens of charges, including one against Mr Papadopoulos, who served 14 days in prison for lying to the FBI.

Mr Morrison was labelled a "man of titanium" by the US president during his official visit last month. (Patrick Semansky/AP)

Today's revelations, if proven true, would amount to Mr Trump asking Mr Morrison to investigate Mr Downer despite his record as Australia's longest-serving Foreign Minister and a former leader of the Liberal Party.

"The Australian Government has always been ready to assist and cooperate with efforts that help shed further light on the matters under investigation," an Australian government spokesperson said this morning.

"The PM confirmed this readiness once again in conversation with the President."

Mr Morrison campaigned with Mr Downer's daughter Georgina during the recent election, where Ms Downer was a candidate for the Liberal Party.

Mr Downer today said he had no knowledge of the call between the two leaders.

"I had a conversation with this guy and I passed on one element of the conversation to the Americans. There's just nothing more to it," Mr Downer told ABC radio.

"I know nothing about conversations about that Scott Morrison has had with the Americans, including President Trump, about this."

A conversation between a Trump aide and Alexander Downer triggered the investigation into collusion between Russia and the president's campaign. (AAP)

Australia and the United States form two members of Five Eyes, an alliance based on the sharing of intelligence with a focus on national security.

There is no date given for the phone call between Mr Trump and Mr Morrison, however the report comes just days after Mr Morrison became just the second foreign leader to be granted a state dinner by the Trump administration.

Mr Trump described Mr Morrison as "a man of titanium" and Mr Morrison appeared at an impromptu campaign rally for the president.

"Together we're making jobs great again," Mr Morrison said, echoing the president's election slogan.

Just days later Mr Trump became just the fourth president to have impeachment inquiry proceedings opened against him.

The opposition Democratic party launched the inquiry following a separate phone call in which the president pushed Ukraine's leader to investigate former vice president Joe Biden and his son.

Mr Biden is the current frontrunner to run against Mr Trump in 2020's elections.

A whistleblower report accused White House officials of storing records of the phone call in a classified server for protection.

Today's report suggests the same action may have been taken with the phone call with Mr Morrison.

White House officials say the practice began, in part, because of the leaking of a contentious phone call between the president and Malcolm Turnbull in 2017.

LETTER REVEALS AUSTRALIA OFFERED TO HELP

A May 28 letter from Australia's Ambassador to the US Joe Hockey reveals he offered Australia's assistance to the investigation into the origins of the Russia probe.

Mr Hockey's letter, obtained by 9News political editor Chris Uhlmann, mentions Mr Downer by name and contains an offer to provide "all relevant information" to the investigation.

"I refer to President Trump's announcement on 24 May that you will investigate the origins of the FBI's probe into Russian links to the 2016 US election," the letter reads in part.

"I note that the President referred to Australia, the United Kingdom and the Ukraine as potential stakeholders.

"Moreover, I note that he has declassified intelligence material to support your investigation.

"The Australian Government will use its best endeavours to support your efforts in this matter.