He has also again threatened to attack a site associated with the Islamic Republic's nuclear program after the two sides launched their biggest wave of attacks on shipping since the start of the six-month-old war.
Tensions in the region were high, with Saudi civil defence authorities on Thursday issuing emergency alerts in the southwest city of Khamis Mushait for the fourth time in 24 hours, as clashes flared with Yemen's Iran-backed Houthis.
Brent crude prices hovered above $US100 a barrel as supply routes through both the Strait of Hormuz and the Red Sea remained heavily disrupted.
Iran said it had attacked 10 ships near the Strait of Hormuz on Wednesday after the US sank five Iranian oil tankers, the latest in a series of tit-for-tat strikes that have signalled scant chance of an imminent end to hostilities.
The war and subsequent increase in fuel prices have helped drive Trump's popularity to record lows. The president said Tehran was trying to influence the November US midterm elections, which will determine whether his Republican Party retains control of Congress.
"I think war is going to end immediately after the election because they can't hold out any longer. They're desperate to try and affect the election," Trump told reporters on Wednesday.
Trump has previously set deadlines for the war to end.
The Wall Street Journal reported later that top White House advisers, including Vice President JD Vance and Secretary of State Marco Rubio, have privately warned Trump the conflict could extend through the remainder of his presidency, which ends in January 2029.
Trump also said the US may hit Iran's Pickaxe Mountain, a heavily fortified site that hosts two deeply buried tunnel complexes near Iran's damaged Natanz uranium enrichment facility.
"We notice there's a little activity at Pickaxe. I would advise Iran not to get cute because we will have to hit them very hard," Trump said in a speech at the midterm Republican convention. Trump has been threatening strikes on Pickaxe Mountain since at least mid-July.
The US and Israel launched military strikes on Iran in February partly due to concerns over Tehran's nuclear program.
Iran says its nuclear activities are for peaceful purposes.
In recent weeks Washington had cited increasing success guiding tankers through the Strait of Hormuz, which carried about a fifth of oil supplies before the war.
But a resumption of fighting this month appears to have set back any such gradual reopening. Just seven vessels transited the strait on Wednesday, half the 10-day average, preliminary ship-tracking data showed on Thursday.
Fighting between Saudi Arabia and the Houthis in Yemen has also escalated in the past few days, a second theatre of war that threatens global energy supplies from the Middle East.
At least 73 people were wounded in four southern Saudi cities, including Khamis Mushait, in recent Houthi attacks on the world's largest oil exporter, the Saudi-led coalition said on Tuesday.
The militant group said it attacked an air base in the southwestern city of Khamis Mushait and oil infrastructure in nearby cities in one of the biggest attacks on Saudi Arabia since the start of the US-Israeli war on Iran in February.
Saudi civil defence authorities issued an all-clear on Thursday following another emergency alert declared in Khamis Mushait.
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