US Central Command said it had struck missile and drone storage facilities and coastal radar positions on Friday.
It said the strikes were in response for a drone attack on a cargo ship on Thursday, an incident which halted a planned evacuation of thousands of sailors stuck in the region.
Tehran said the cargo ship was attacked because it was using an unauthorised route to transit through the vital Gulf waterway.
US Central Command - or Centcom - described the strikes as "a powerful response" to the drone attack a day earlier.
"The unwarranted aggression against commercial shipping by Iranian forces clearly violated the ceasefire," it said in a statement.
"Furthermore, Iran's dangerous behavior undermined freedom of navigation as commerce increasingly flows through the vital international trade corridor."
Centcom said the US military would "continue to provide safe passage coordination and support to commercial vessels transiting the strait".
But Iran's Islamic Revolutionary Guard Corps (IRGC) blamed the "treaty-breaking US regime".
It said in a statement the US had launched an airstrike on Iran's coast "under various pretexts of a ship violating an unauthorised route in the Strait of Hormuz".
The IRGC said its navy had retaliated by striking US military positions in the region, without providing further details. The BBC contacted the Pentagon for comment.
"If the aggression is repeated our response will be more extensive than this," the IRGC added.
Tehran effectively closed the strait after US and Israeli attacks against Iran began at the end of February.
The shutdown of the critical waterway for oil and gas shipments caused a spike in global oil prices and choked off shipments of other crucial commodities such as fertiliser.
The US and Iran agreed on 17 June to end hostilities under a 14-point memorandum of understanding, which had also called for Iran to use its "best efforts for the safe passage of commercial vessels with no charge for 60 days".
In a post on X following the US retaliatory strikes, Vice-President JD Vance said that if Iran "has disagreements about how the MOU is being applied, they can pick up the phone".
"But violence will be met with violence," he added.
Ebrahim Azizi, head of the Iranian parliament's national security commission, though, said on social media that the US had "attacked Iran in the middle of negotiations once again".
He continued in his social media post: "This reckless violation of the ceasefire will, as always, lead to retreat and regret on their part. The blame game does not work anymore."
Speaking to reporters at the White House on Friday afternoon, Trump refused to be drawn into questions on how the US might respond to the drone attack, or whether he viewed the ceasefire as still intact.
"You'll find out," he said. "I don't like the fact that they took a shot yesterday. They shouldn't be doing that."
Asked why he believed Iran would conduct such an operation, Trump said only that "they're a little bit different".
In recent days, Trump and other US officials insisted negotiations with Iran were progressing well, saying Iran had given up any suggestion of tolling vessels transiting through the Strait of Hormuz.
In a Truth Social post on Wednesday, Trump said Iran had informed the US that there would be "no tolls, no insurance costs and no other charges of any kind being sought or received".
"If this is false information, negotiations would end, immediately," he added.
The US has condemned reports that Iran is charging fees to tankers going through the strait, and many see any tolling system as breaking with international maritime law.
On Tuesday, Iranian and Omani officials held talks in Oman's capital of Muscat to discuss "the future management of navigation", although Omani Foreign Minister Badr Al-Busaidi said both countries were committed to "toll-free safe passage".
However, Iran's chief negotiator, Mohammed Bagher Ghalibaf, told state-affiliated news outlets that "everyone should know that the administration of the Strait of Hormuz will never go back to the way it was before the war."
The cargo ship hit by a projectile on Thursday was the Ever Lovely, a Singapore-flagged vessel.
According to British maritime security agency UKMTO, the ship was struck 7.5 nautical miles south-east of Oman's port of Dahit.
The Ever Lovely had been following the UKMTO's recommended route through the strait when it was struck, the ship's owner, Evergreen, said.
"All crew members remain safe as does the vessel itself and all cargo," it added.
In response, the UN's International Maritime Organization (IMO) paused its planned evacuation of more than 11,000 sailors who have been stranded in the key shipping lane since the war erupted.