Vowing to retaliate for what it called a deadly attack, Iran later said it had launched missiles at US sites in Jordan.
Forces with the Revolutionary Guard Corps were observed preparing to launch rockets with sea mines into the strait, according to Tim Hawkins, a spokesperson for the US Central Command.
The US military last week completed clearing sea mines from the strait's international shipping routes.
Semiofficial news outlets in Iran reported sounds of explosions near Larak island in the strait on Sunday. The Guard in a statement carried by Iran's state broadcaster noted "the martyrdom and injury of several of our fighters and compatriots".
Later, Iranian state television showed what it said were ballistic missiles being fired by Iran at US bases in Jordan in response to the American strikes.
Jordan's armed forces said they intercepted eight missiles that penetrated the country's airspace early on Monday.
US military officials disputed Iran's claim that the latest American strikes were an act of aggression, calling them a "limited, precise action" against what they said were mine laying forces.
"In essence, Iran created the threat and the US military eliminated it to protect civilian mariners, commercial shipping, and the free flow of global commerce," US Central Command said in a statement late Sunday.
A return to open conflict would be dangerous for the region, where Iran has targeted US military bases and infrastructure in Gulf countries since the war began on February 28.
The last time the US military confirmed targeting Iran was on July 29, when it announced a "heavy wave of strikes" on dozens of Revolutionary Guard targets including coastal surveillance and defence sites.
On August 1, US President Donald Trump said he would order the military to hold off on new strikes at the urging of Gulf allies Qatar, Saudi Arabia and the United Arab Emirates.
The attack comes just days after the Trump administration said it would turn its focus to increasing economic pressure - rather than military action - to try to end its war with Iran. The shifting strategy centres on threats to punish any country or entity that continues to conduct business with Tehran.
Sunday's attack was a "fatal mistake by the Trump regime during the economic war" and the enemy will pay the consequences militarily and economically, a Guard spokesperson, General Hossein Mohebi, said in a statement carried by Iranian media.
The US turn to using sanctions came as the administration weighs diminished munitions stockpiles after months of war, sparking concerns that the prolonged conflict could undermine US military readiness in other parts of the globe.
As the conflict grinds on, Trump's talk of finding a quick end to the war also appears to be fading.
He stressed last week that he's "not in a hurry" to get Iran back to the negotiating table, and he continues making the case that the Islamic Republic's leadership is on the ropes.
Appointments to Iran's senior security leadership in the past month, however, have signalled Tehran's defiance after weathering decades of sanctions as well as a lack of tolerance for dissent at home.
Trump has consistently emphasised that the US and Israeli campaign has been devastating for Iran's navy and air force.
Iranian officials have said the country has suffered $US270 billion ($A377 billion) in direct and indirect damage. Israeli military strikes in the first weeks of the war wiped out much of the theocratic government's leadership structure.
But Iran has found leverage through its strikes against vessels on the Strait of Hormuz, where relatively few ships carrying oil and liquefied natural gas are risking passage. Iran still has enough drones and missiles to fire at vessels transiting the waterway through which 20 per cent of the world's oil normally flows.
Crude oil prices rose on Sunday in response to the US attack.
The price for a barrel of US oil went up 1.8 per cent to $US84.94 ($A118.65), while the price for a barrel of Brent crude, the international standard, rose 1.9 per cent to $US89.79 ($A125.42).
with dpa
