U.S. President Donald Trump speaks to reporters before leaving the White House on Aug. 9, 2019. (Xinhua/Ting Shen)

US President Donald Trump has warned "a whole civilisation will die tonight" unless Iran reaches a deal on reopening the Strait of Hormuz.

The US president adds that "something revolutionarily wonderful can happen" before his deadline. Trump has given Iran a deadline of 20:00 EDT Tuesday (00:00 GMT / 01:00 BST on Wednesday) to reopen the Strait of Hormuz. 

"I don’t want that to happen, but it probably will. However, now that we have complete and total regime change, where different, smarter, and less radicalised minds prevail, maybe something revolutionarily wonderful can happen. WHO KNOWS?," Trump said.

"We will find out tonight, one of the most important moments in the long and complex history of the world. 47 years of extortion, corruption, and death, will finally end. God bless the Great People of Iran!"

Meanwhile the US has carried out new strikes on military targets on Kharg Island, Iran's key oil export terminal Israel warns Iranians not to travel by train - saying it "endangers your life" - and also confirms an attack on a third petrochemical site.

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The number of people killed in Iran since the US-Israeli attacks began is over 3,500, including at least 1,665 civilians, a US-based human rights group says.

Meanwhile, Iran says it has formally rejected a US ceasefire proposal, state media reports – while sharing a list of demands.

In a new statement, Iran's Islamic Revolutionary Guard Corps (IRGC) says it has shown "considerable restraint" and "exercised care in selecting targets for retaliation" against the US and its regional partners.

"From this point forward, all such considerations will be set aside," it says in a statement shared on state-run media.

The IRGC also says that if the US military "crosses red lines, our response will go beyond the region" – adding that it will target the US and its partners' infrastructure and disrupt regional oil and gas supplies for years.

Iran rarely responds to overt threats and ultimatums in the way some people might expect.

Having managed to survive more than a month of devastating airstrikes and precision bombing by two of the world’s most powerful militaries, the Islamic Republic is in no mood to make concessions.

It’s hurting, there is no doubt about that, but partly due to its ideology of martyrdom its pain threshold is far higher than that of Western nations.

Donald Trump will be hoping that his expletive-laden threat to bomb Iran "back to the Stone Ages" will be enough to terrify Tehran into releasing its chokehold on the Strait of Hormuz.

But this is Iran’s strongest card and it’s not going to give it up without a permanent end to this war - plus other demands like ending Israel’s war on Hezbollah.

Meanwhile, Iran has made clear that whatever civilian infrastructure the US targets on Tuesday night it will correspondingly target in the Gulf states.

So Kuwait, Bahrain, Saudi Arabia, the UAE and possibly Qatar will be bracing themselves if Trump makes good on his threat.