U.S. President Donald Trump told Australia's ambassador Kevin Rudd that he didn't like him and "probably never will" during a White House meeting with the Australian Prime Minister.

Rudd, a former Australian Prime Minister, has been sharply critical of Trump in the past.

During Monday's meeting a journalist asked Trump if he had any concerns about the current Australian administration and Rudd's previous comments.

The U.S. President said he knew nothing about the ambassador, asking Australian Prime Minister Anthony Albanese if he still worked for him, only to realise Rudd was sitting directly opposite him.

"You said bad?" he asked the diplomat to which Rudd replied: "Before I took this position Mr President."

"I don't like you either, and I probably never will," Trump said in response to a round of laughter from journalists in the room.

The two countries signed a critical-minerals deal at the meeting, as the U.S. eyes the continent’s rich rare-earth resources at a time when China is imposing tougher rules on exporting its own critical minerals abroad.

The two leaders described the agreement as an $8.5 billion deal between the allies.

Trump said it had been negotiated over several months.