US President Donald Trump called Australian PM Scott Morrison and asked for his help with an investigation into the origins of the Mueller inquiry, Australian officials have confirmed.
Mr Morrison was asked to help find evidence to discredit the inquiry, according to US and Australian media.
Australia confirmed the call had taken place and that the PM agreed to help.
The revelation came as Mr Trump faced impeachment proceedings at home over a call with another foreign leader.
The president has been accused of pressuring the leader of Ukraine to investigate domestic political rival Joe Biden, in a phone call which was exposed by a whistleblower last week. The call spurred Democrats to launch impeachment proceedings and on Monday the president's lawyer Rudy Giuliani was served with a subpoena.
At the White House end, the transcript of the call between Mr Morrison and Mr Trump was restricted to a small number of the president's aides, reports said - contrary to normal protocol. The same restrictions were reportedly placed on the Ukraine call, raising concerns that White House staff were attempting to conceal records of the president's conversations with certain foreign leaders.
The Mueller inquiry investigated whether Mr Trump colluded with Russia in the 2016 presidential election. Its findings, released in April, did not establish that the Trump campaign criminally conspired with Russia to influence the election.
But the findings did not exonerate the president of collusion, and the Mueller report outlined an extensive obstruction-of-justice case against the president.
The inquiry infuriated Mr Trump and he relentlessly criticised it as a "witch hunt". In May he announced that the US Attorney-General William Barr would look into how the inquiry originated.
Australia's ambassador to the US, Joe Hockey, wrote to the White House shortly afterwards offering to help with any review, Australian media reported.
In a statement on Tuesday, the Australian government said it had "always been ready to assist and co-operate with efforts that help shed further light on the matters under investigation".
"The PM confirmed this readiness again," the statement said.
Australia's conservative leader is among Mr Trump's closest international allies and received the rare honour of a state dinner at the White House last week.
The call which discussed the Mueller investigation took place shortly before that visit, according to the New York Times.
What is known about Australia's link?
The Trump-Russia investigation was partly triggered by Australian officials communicating a top diplomat's concerns to the FBI.
Alexander Downer, then Australia's High Commissioner to the UK, said former Trump adviser George Papadopoulos had told him in May 2016 that Moscow had incriminating "dirt" on Hillary Clinton.
"He said... that the Russians might release some information which could be damaging to Hillary Clinton," Mr Downer later told the Australian Broadcasting Corporation.
Mr Papadopoulos denies ever discussing such details. He served a two-week jail sentence in 2018 after pleading guilty to lying to the FBI about meetings he had with alleged go-betweens for Russia.