Iranian state television reported explosions were heard on Qeshm Island on Monday.
A US official who wasn't authorised to comment publicly and spoke on condition of anonymity, said the strikes targeted "Iranians using surface to air missiles against US assets".
Fox News, citing officials, said the strikes were defensive and carried out in response to Iran firing at a US aircraft.
The strikes appeared to be limited as opposed to a return to full hostilities but followed President Donald Trump saying the US wouldn't launch strikes on Iran before Tuesday's midterms.
Asked by reporters if he was considering striking Iran after Tuesday's midterm elections, Trump replied "no".
The unpopular Iran war and the resulting impact on US fuel prices and other parts of the economy have been a vulnerability for Republicans struggling to keep control of Congress.
The administration was last known to have carried out some attacks in early September, but thousands of US troops remain in the waters off Iran to maintain a naval blockade aimed at preventing tankers carrying Iranian oil from getting to the global market.
Plus, a third aircraft carrier and thousands of additional troops are on their way to the Middle East.
Earlier on Monday, US Vice President JD Vance offered measured optimism that a deal could still be struck to prevent Trump from following through on his threat to order new strikes on Iran after the midterm elections.
Vance sent a letter to Iran's security chief, Mohsen Rezaei, last week.
Trump told reporters that letter was focused on assisting Iran with "medical supplies and various things".
But Vance suggested there's reason to believe that the US and Iran could still come to an agreement.
"We've had a number of good conversations with the Iranians," Vance told reporters.
"The president and I both feel pretty good about the prospects for potentially coming to a negotiated settlement. We're going to keep on working at it."
Vance's comments came as the region remains on edge about the prospects of the US resuming full-scale operations against Iran.
The backchannel efforts are playing out as Israel and some Middle East allies lobby Trump on the way ahead in the eight-month-old war that's rattled global markets and wreaked havoc on Iran.
Trump noted a drop in oil prices in his final midterm election speech in Washington on Monday, seeking to minimise the scale of the conflict, which has cost US taxpayers at least $US47 billion ($A67 billion).
"I don't know if you even call it a war, because we haven't been doing any fighting for months," Trump said.
with Reuters
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