Iran said its forces attacked a US naval drone trying to enter the Strait of Hormuz, hours after targeting ships in retaliation for American strikes on three oil tankers.
The latest round of clashes, which began with US raids last week, comes amid a deadlock in their six-month war.
Iran has maintained its stranglehold on the strategic Strait of Hormuz while Washington continues a counter-blockade of Iranian ports.
Washington is also seeking to choke Iran's economy, rolling out sanctions on entities with financial links to the Islamic republic in a bid to force it into submission.
The Islamic Revolutionary Guard Corps, the ideological arm of Iran's military, said today that it "attacked an American military unmanned surface vessel" attempting to enter the strait, according to a statement carried by state television.
Hours earlier, the IRGC said its naval forces "targeted three oil tankers on the unauthorised route of the Strait of Hormuz and three vessels affiliated with the child-killing America in other areas".
It warned ships not to attempt to transit by unapproved routes.
Yesterday, US Central Command (CENTCOM), which oversees American military operations in the region, said it struck tankers linked to the Iranian Guards, accusing the most powerful arm of the Iranian military of unsuccessfully firing at American warships.
"Following Iran's failed attacks, CENTCOM permanently disabled the IRGC crude oil carriers M/T Downy off the coast of Kharg Island and M/T Stark 1 near Jask," it said.
"American forces also completely destroyed the unladen crude oil carrier M/T Kylo ...
in the Gulf of Oman, striking the vessel in multiple critical locations to render it inoperable after the crew was directed to abandon ship," he said.
Video posted by CENTCOM showed large fireballs and billowing flames after projectiles slammed into the ships.
The three vessels were "part of a multibillion-dollar shadow network that funds the IRGC and its regional proxies", it said.
'Higher economic cost'
The IRGC meanwhile claimed the two American warships they targeted had been "forced to retreat" after "suffering damage", but CENTCOM said those ships successfully evaded Iranian attacks.
CENTCOM commander Admiral Brad Cooper said after the operation: "If you shoot at two of our ships, we will impose an even higher economic cost - taking out three of yours."
The Iranian foreign ministry hit out at Washington over the strikes on oil tankers, calling them "illegal and aggressive actions".
A correspondent for Iranian state TV in Jask in the southern province of Hormozgan said one of the tankers was empty and the second was carrying oil.
The crews were transported to shore on lifeboats, they said.
Another state TV correspondent on Kharg Island said the attack there caused no casualties.
Iran's Khatam-al Anbiya central military command warned that if the US continued its attacks, then Tehran's retaliation against US warships would be "more severe than before, and there is a possibility of their expansion".
The administration of US President Donald Trump has tried to downplay the significance of the six-month conflict, which has proven increasingly unpopular at home as midterm elections near.
US Vice President JD Vance went so far as to say that he "wouldn't call it a war".
Mr Trump reiterated that view on Friday, calling the war "small potatoes" for Washington.
Iran's Security Chief Mohsen Rezaei warned this week that the Islamic republic had adopted a "new strategy" against Washington that "will shatter your foundations".
The US has been trying to step up pressure on Tehran in a bid to wrestle control of the Hormuz strait, through which one-fifth of world oil supplies previously flowed.
A fragile ceasefire between the two sides collapsed in July after attacks on commercial ships in the strategic waterway.
Mr Trump has in recent weeks repeatedly threatened to claim sovereignty over the strait, even posting a map showing it as "new US territory".
Mr Vance has insisted the US will not reopen talks with Iran until it ends attacks on commercial shipping in Hormuz.