Graham added that those efforts by American officials included “accepting information from an Australian diplomat who was … directed to contact [Trump campaign foreign policy adviser George] Papadopoulos and relay information obtained from Papadopoulos regarding the campaign to the Federal Bureau of Investigation.”

It has been reported that Papadopoulos had revealed to an Australian diplomat, believed to be Alexander Downer, details of his April 2016 conversations with Josef Mifsud, a London-based professor with ties to the Kremlin. Mifsud allegedly told Papadopoulos that Moscow had “thousands of emails” damaging to 2016 Democratic presidential nominee Hillary Clinton.

In a letter responding to Graham dated Wednesday, Ambassador Joe Hockey wrote that the Australian government “is cooperating” with Barr’s inquiry and has “been public about our willingness to cooperate.”

Hockey added: “In your letter you made mention of the role of an Australian diplomat. We reject your characterisation of his role.”

According to Mueller’s report, a foreign government official contacted the FBI in July 2016 about an encounter he had with Papadopoulos two months earlier, during which the then-Trump aide suggested the campaign “had received indications from the Russian government that it could assist the Campaign through the anonymous release of information damaging to” Clinton.

That warning “prompted the FBI on July 31, 2016, to open an investigation into whether individuals associated with the Trump Campaign were coordinating with the Russian government in its interference activities,” Mueller wrote.

Papadopoulos was sentenced in September 2018 to 14 days in federal prison for making false statements to the FBI.

The New York Times reported Monday that Trump pushed Australian Prime Minister Scott Morrison in a recent telephone call to help Barr gather information for the Justice Department's inquiry.