US President Donald Trump has warned Iran that “the clock is ticking” amid reports that America and Israel are prepping to resume attacks.

Trump wrote on Truth Social that Iran “better get moving, FAST, or there won’t be anything left of them.

“TIME IS OF THE ESSENCE! ” he posted to social media on Sunday (Australian time).

A day earlier Trump posted an AI-generated image of himself on a military vessel with the cryptic headline: “It was the calm before the storm.”

Trump posted this digital image, amid reports the US is set to resume hostilities with Iran.

It comes amid a report that the Israeli military had been put on high readiness for a potential resumption of attacks on Iran, according to Israel’s Yedioth Ahronoth newspaper.

Citing government sources, the report says Israel is awaiting a decision from Trump.

It said signs were increasing that Trump had concluded that Tehran was not prepared to accept his conditions for an end to the war.

Yedioth Ahronoth reported that the US and Israel were preparing intensively for a resumption of hostilities.

Earlier, The New York Times reported that the Pentagon was preparing to restart the war because Washington’s original aims had not been achieved, especially for Tehran’s nuclear program.

The US and Israel were engaged in intense preparations for the possible resumption of attacks against Iran as early as this week, according to the Times, citing two Middle East officials.

Israel’s N12 television broadcaster reported that Trump was thought likely to convene advisers soon after his return from China to take a decision on resuming hostilities.

N12 said that the Israeli government believed a decision on a military campaign lasting “days up to weeks” could be taken “very soon.”

According to Yedioth Ahronoth, Trump is not believed to be planning a full-scale war aimed at toppling the Iranian government.

Instead, he is thought to be considering limited strikes on power stations and bridges, it said.

Ground operations to seize the key oil export terminals on Kharg Island in the Gulf or to recover an estimated 440 kilograms of uranium enriched to 60 per cent held by Iran are also conceivable, according to the report.

-with AAP