The latest escalation on Wednesday comes days after a fragile truce collapsed, raising the spectre of a return to full-scale war, though analysts generally see that as less likely. Hostilities have intensified since Iran said late on Saturday it had closed the Strait of Hormuz.
Military operations are also keeping ships from transiting the vital artery, which carried about a fifth of global oil and gas shipments before the war. Brent crude oil, the international benchmark, closed at a one-month high of $US84.95 ($A121.36) a barrel on Wednesday.
US Central Command said the military had attacked coastal defence systems and cruise missile storage and launch sites on Iran's Greater Tunb Island, and had completed the wave of strikes within around 90 minutes.
Nine hours later, Central Command reported a second wave of strikes.
The strikes are targeting Iranian military capabilities used to threaten vessels freely transiting through the Strait of Hormuz, an international waterway vital to global commerce.
"The US military is holding Iran accountable at the Commander in Chief's direction," Central Command said on X.
Three US officials told Reuters that US strikes aimed at forcing open the strait are also targeting Iranian military capabilities the US would want to destroy before executing more complex operations.
The US military also said it disabled an unladen oil tanker attempting to sail toward Iran's Kharg Island after it ignored multiple warnings, firing Hellfire missiles into the ship's smokestack. Since resuming a naval blockade against Iran on Tuesday, the US has redirected two ships and disabled another, the military said.
The Islamic Revolutionary Guard Corps on Wednesday said it had struck US military targets in the region, including in Bahrain, Kuwait and Jordan. Kuwait said its armed forces intercepted four missiles and 21 drones from Iran on Wednesday in an attack that caused material damage but no injuries.
The war has killed thousands of people and displaced millions, mainly in Iran and Lebanon, where conflict restarted between Israel and Iran-backed militant group Hezbollah. In July alone, US attacks have killed 35 people, Tasnim reported, citing a health ministry official.
President Donald Trump struck a triumphant note, as he has repeatedly since the US and Israel started hostilities on February 28, saying, "We'll have Iran defeated soon. They'll be defeated very soon."
Speaking at a roundtable event at the Pennsylvania Defence and Innovation Summit, Trump also claimed the Iranians want to "settle so badly".
"They don't like what we're doing, and they do want to settle. We'll find out whether or not we settle with them, or we just finish it off," he said.
On Tuesday, Trump said US negotiators had been in touch with their Iranian counterparts to tell them "you better make a deal."
Iran's military spokesperson said that the only way to reopen the Strait of Hormuz was for the US to comply with the 14-point memorandum of understanding that the two sides signed in June, and the implementation of "Iranian regulations" regarding ship traffic in the strait.
Even amid the hostilities, there was a possible sign of goodwill. Trump said Iran had allowed an American who was "wrongfully detained" under the Biden administration in 2024 to leave the country.
"The United States of America appreciates this gesture of Goodwill by Iran," Trump wrote on Truth Social.
Human rights lawyer Jared Genser identified the released American as Dena Karari, who had been prevented from leaving Iran since December 2024.
"Dena is now safe and travelling back to the United States," Genser wrote on X, thanking Trump for his efforts to free her.
