Officials have stopped short of ruling out that US strategic bombers are carrying nuclear weapons to Australia, but the government insists any such move would not breach this country's international obligations. 

During a Senate estimates hearing on Wednesday Greens senators sought details on whether visiting American aircraft such as the B-52s operating out of the Top End are ever nuclear armed.

The committee was told the United States had a longstanding policy of "neither confirming or denying" the presence of nuclear weapons under its practice of maintaining global operational unpredictability. 

US bomber aircraft have been visiting Australia since the early 1980s, with nuclear-capable B-52s and B2 Sprits regularly operating out of northern Australia.

Defence Department secretary Greg Moriarty said the "stationing of nuclear weapons" in Australia was prohibited under the South Pacific Nuclear Free Zone Treaty, but the treaty did not prevent visits by the US bombers.

"Successive Australian governments have understood and respected the longstanding US policy of neither confirming nor denying the presence of nuclear weapons on particular platforms," he said.

"Australia will continue to fully comply with our international obligations. And the US understands and respects Australia's international obligations with respect to nuclear weapons."

Foreign Minister Penny Wong backed the secretary's statement and accused Greens senators of trying to "make a political point". 

"This is the Australian position: We understand and respect the longstanding US policy of neither confirming or denying. That is the position," Senator Wong said.

"But we remain fully committed to the South Pacific Nuclear Free Zone Treaty, and we will fully comply with our international obligations, which are understood by the United States."

Under further questioning from Greens senator David Shoebridge, the foreign minister said it would not be appropriate to elaborate. 

"The responsible way of handling this is to recognise that the US has a neither-confirm-nor-deny position, which we understand and respect," she said.

Shadow Defence Minister Andrew Hastie said the possible temporary presence of nuclear weapons in Australia was a matter for the government of the day.

"We have a very strong relationship with the United States, and of course those decisions are for the government of the day," he said.

"And of course we want to see a greater presence of the American military in the Indo-Pacific. They've provided great support to the region."

Defence mulls methods to make warships more deadly

Defence has also revealed it is examining ways to make Australia's next fleet of warships more lethal. 

A recent Australian National Audit Office report has criticised progress on the British-designed Hunter class frigate program and warned it could be outgunned by enemies.

Chief of Navy Vice Admiral Mark Hammond told senate estimates Defence was considering plans to add further weapons to the future warship.

"Like the rest of the surface combatant force, we are looking at options to increase the lethality of its offensive suite as well," he said.