President Donald Trump says Operation Epic Fury is “nearing completion” but first the US will bomb Iran hard over the next few weeks and “send them back to the stone ages”.

Trump told America in a rambling televised speech on Thursday (AEDST) that the US military ‌had nearly completed its objectives in Iran and the conflict would soon be ending.

“We are going to finish the job, and we’re going to finish it very fast. We’re getting very close,” he said.

He added later: “We’re going to hit them very hard over the next two to three weeks.

“We’re going to bring them back to the stone ages where they belong.”

Trump, facing a war-wary US public and sliding approval ratings, said Iran’s navy was “gone”, its army was in “ruins”, its leaders had “perished” and its weapons factories were “blown to pieces”.

“Never before in the history of warfare has an enemy suffered such clear and devastating large-scale losses in a matter of weeks,” he said.

Trump said the US was close to achieving its objectives.

He said regime change was not one of  his goals but he claimed it had been achieved and the new leadership was “less radical and more reasonable”.

Trump and his advisers have offered shifting explanations and timelines for the conflict, now in its fifth week. ⁠

Most Americans oppose the conflict and are upset at rising petrol prices which hit US$4 a litre on Thursday (AEDT).

The president briefly addressed those concerns, mainly to say that petrol prices would soon go down, that it was a worthwhile short-term sacrifice and that it was mainly Iran’s fault.

“This short-term increase has been entirely the result of the Iranian regime launching deranged terror attacks against commercial oil tankers of neighbouring ​countries that have nothing to do with the conflict,” Trump said.

He said the US imported almost no oil through the Strait of Hormuz, but urged nations that did to take the lead to “get the oil they so desperately need”.

When the war was over, he said the strait would “naturally reopen”.

And he notably suggested the war could escalate if Iranian leaders did not capitulate to US terms during negotiations.

If Iran did not come to  deal, Trump said the US would hit its electric generating plants “very hard and probably simultaneously”.

He asked Americans to keep perspective about a war now ⁠in its fifth week, pointing out that the conflict was much shorter than the ‌country’s involvement ​in several previous wars.

No clear case for longer war

Speaking shortly after Trump’s presidential address, Prime Minister Anthony Albanese questioned what more was left to achieve in the war, warning greater economic damage would be inflicted if the conflict dragged out.

“It is not clear what more needs to be achieved or what the end point looks like,” he told the National Press Club on Thursday (AEDT).

“What is clear is that the longer the war goes on, the more significant the impact on the global economy will be.”

Asked if Trump has damaged the social licence for the AUKUS security pact with the US and UK, Albanese said Washington remained Australia’s most important ally.

“People will have different views … my job as Australian prime minister is to develop relationships with world leaders,” the Labor leader said.

“That’s what I do and that is what I have done.”

Foreign Minister Penny Wong will meet with her counterparts from 35 nations, including Italy, France, Germany and Japan, in a virtual meeting on Thursday.

The US has not been invited.

Defence Minister Richard Marles said the nations would assess what contributions could be made to restore navigation in the strait.

-with AAP