President Donald Trump shakes hands with Australian Prime Minister Scott Morrison in the Oval Office of the White House, Sept. 20, 2019, Washington. AP

Canberra, Australia — Australia's prime minister has said that his country was unlikely to provide the United States with internal government communications with an Australian diplomat who is partially responsible for triggering the FBI investigation into Russian interference in the 2016 American presidential election. President Trump recently asked Prime Minister Scott Morrison and other foreign leaders to help U.S. Attorney General William Barr with a review of the origins of the Russia probe that was triggered in part by a tip from Australia's top diplomat in Britain, Alexander Downer.

Barr asked Mr. Trump to call Morrison to alert him that the attorney general would be reaching out, a Justice Department official confirmed to CBS News. Morrison agreed to cooperate with the inquiry during a phone call with Mr. Trump last month, which Morrison described as a "fairly uneventful conversation," but Morrison said Wednesday that Australia was unlikely to provide Downer's diplomatic communications about the matter to U.S. investigators.

"It would be a very unusual thing to do and Australia would never do anything that would prejudice our national interest," Morrison told Sky News Australia.

In May, Australia's ambassador to Washington formally offered Australia's help with the Justice Department's review of the origins of the Mueller report. It is unclear what, specifically, the U.S. has sought from Australia.

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Morrison said Wednesday that Mr. Trump did not phrase the request as a "favor" during their call, and that "it would have been, I think, frankly more surprising had we chosen not to cooperate."

Mr. Trump's interactions with foreign leaders, and Barr's role in those discussions, are under heightened scrutiny now that the U.S. House of Representatives has launched an impeachment inquiry into the president.

Morrison's political foes in Australia have questioned whether the prime minister is drawing Australia into a U.S. domestic political battle and have demanded a transcript of his phone conversation with Mr. Trump.

Foreign Minister Marise Payne said the U.S. government would have to be involved in any decision to release a transcript of the call.