SYDNEY, March 20, 2024 (BSS/AFP) - Australia insisted Wednesday that its ambassador to Washington was doing a "good job" after Donald Trump suggested he was "not the brightest bulb" and could be expelled from the United States.

Trump lashed out during a TV interview at former prime minister-turned-diplomat Kevin Rudd, who has been critical in the past of the bombastic former US president.

When prompted to comment on Rudd, Trump said he had heard he was "a little bit nasty".

"I hear he is not the brightest bulb," Trump said, adding that "if he is at all hostile, he will not be there long".

Trump is currently the frontrunner to win November's US presidential election, although polls suggest the race against incumbent President Joe Biden could be very close.

An Australian government spokesperson defended Rudd, telling AFP he was "doing a good job as Australia's Ambassador to the United States".

Rudd, who took up the diplomatic role in March 2023, had previously described Trump as "nuts", "the most destructive president in history", and a "traitor to the West".

A fluent Chinese speaker, Rudd's tenure has focused on deepening defence collaboration under the AUKUS agreement -- a security pact between Australia, Britain and the United States.

The agreement would see Australia develop nuclear-powered submarines and a host of other advanced US weaponry.

Democratic congressman Joe Courtney said on X, formerly Twitter, that Rudd's appointment had strengthened relationships between the countries.

"He is respected & admired by legislators on both sides of the aisle-a rare feat in D.C," he wrote.

Trump was also asked during the GB News interview about whether Prince Harry should receive "special privileges" if authorities found he had lied about taking drugs on his US visa application -- something that normally leads to deportation.

"If he lied, we'll have to take appropriate action," Trump warned.