US Defense Secretary General James Mattis has dismissed as 'fiction' an Australian media report claiming American forces were prepared to bomb Iran's nuclear facilities as early as next month.

A bewildered Mattis was quizzed by US reporters in Washington DC on Friday about the ABC report.

The 'exclusive' report quoted unnamed senior Australian government figures and claimed Australian defence facilities would likely play a role in identifying targets in Iran.

US Defense Secretary General James Mattis (pictured) has dismissed as 'fiction' an Australian media report claiming American forces were prepared to bomb Iran's nuclear facilities as early as next month

'I have no idea where the Australian news people got that information,' Mattis told reporters.

'I'm confident it is not something that's being considered right now, and I think it's a complete - frankly, it's - it's fiction.

'It's the best I can give you.'

Mattis' Friday press conference opened with a question about the Australian news report.

The report came after Mattis and US Secretary of State Mike Pompeo met with Australian Defence Minister Marise Payne and Foreign Minister Julie Bishop earlier in the week in California for annual AUSMIN talks

'Can you assure the American people that the US is not preparing military strikes against Iran?' the reporter asked.

The report came after Mattis and US Secretary of State Mike Pompeo met with Australian Defence Minister Marise Payne and Foreign Minister Julie Bishop earlier in the week in California for annual AUSMIN talks.

It also followed heated words exchanged on Twitter and in Iranian news reports between US President Donald Trump and Iranian counterpart Hassan Rouhani.

Australian Prime Minister Malcolm Turnbull also said he had 'no reason' to believe the ABC report was true.