The heightened rhetoric did little to quell a sharp retreat in crude prices and a rally in global shares, which came after Trump expressed confidence in a swift end to hostilities even after Iran appointed Mojtaba Khamenei as its new supreme leader in a signal of defiance.
Trump said on Monday the United States had inflicted serious damage on Iran's military and predicted the conflict would end well before the initial four-week time frame he had laid out, though he has not defined what victory would look like.
Israel says its war aim is to overthrow Iran's system of clerical rule.
US officials mainly say Washington's aim is to destroy Iran's missile capabilities and nuclear program, but Trump has said the war can end only with a compliant Iranian government.
At least 1332 Iranian civilians have been killed and thousands wounded since the US and Israel launched a barrage of air and missile strikes across Iran at the end of February, according to Iran's UN ambassador.
Trump warned that US attacks could rise sharply if Iran sought to block tanker traffic through the Strait of Hormuz, which handles one-fifth of the world's oil supply.
"We will hit them so hard that it will not be possible for them or anybody else helping them to ever recover that section of the world," Trump said at a news conference on Monday.
Iran's Islamic Revolutionary Guards Corps said it would not allow any oil to leave the region if attacks from the United States and Israel continued.
"We are the ones who will determine the end of the war," a spokesman said, describing Trump's comments as nonsense, according to state media.
In a later Truth Social post, Trump repeated his warning.
"If Iran does anything that stops the flow of Oil within the Strait of Hormuz, they will be hit by the United States of America TWENTY TIMES HARDER than they have been hit thus far," he said.
Iranian Foreign Minister Abbas Araqchi said Iran was unlikely to resume negotiations with the US, citing what he described as a "bitter experience" with past talks.
"After three rounds of negotiation, the American team in the negotiation said itself that we made a big progress. Still, they decided to attack us. So, I don't think talking to the Americans any more would be on our agenda any more," he said in an interview with US broadcaster PBS.
The war has already effectively shut the Strait of Hormuz, leaving tankers unable to sail for more than a week and forcing producers to halt pumping as storage facilities fill.
Mojtaba Khamenei's appointment on Monday appeared to dash hopes of a swift end to the war, sending oil markets surging and share markets nosediving before swinging in the other direction when Trump predicted a quick end to the war and reports of a possible ease in sanctions on Russian energy.
After speaking with Russian President Vladimir Putin, Trump said the United States would waive oil-related sanctions on "some countries" to ease the shortage.
The price of petrol has particular political resonance in the United States, where voters cite rising costs as a top concern ahead of the November midterm elections, when Trump's Republicans will try to keep control of Congress.
Tehran was choked in black smoke after an oil refinery was hit, an escalation in strikes on Iran's domestic energy supplies.
Turkey said NATO air defences had shot down a ballistic missile that was fired from Iran and entered Turkish airspace, the second such incident of the war.
Israel's military said it had launched new attacks in central Iran and struck the Lebanese capital, Beirut, where Israel has extended its campaign after the Iran-backed militia Hezbollah fired across the border.
with AP
