As the conflict entered its second day, US President Donald Trump said 48 Iranian leaders had been killed and the US military had started sinking Iran's Navy, destroying nine Iranian warships so far and "going after the rest".
US aircraft and warships have struck more than 1000 Iranian targets since Trump ordered the start to major combat operations on Saturday, the US military said.
US Central Command posted vision of strikes on Iranian targets on X.
"The Iranian regime's reckless use and proliferation of ballistic missiles have been a dangerous threat for decades. Now, at the President's direction, US forces are eliminating the threat," it wrote.
The strikes include B-2 stealth bombers dropping 900kg bombs on hardened, underground Iranian missile facilities.
Iran's retaliatory attacks also started taking a toll, with the US military reporting three US troops had been killed and another five were seriously wounded in US operations against Iran.
US Central Command said several other US troops suffered minor shrapnel injuries and concussions as well. It did not disclose where or how those casualties took place.
Two US officials, speaking on condition of anonymity, told Reuters the US service members were killed on a base in Kuwait.
Trump sought to brace the US public for more casualties as he acknowledged the deaths, the first in major operations since he returned to office last year.
The US bombing of Iran's nuclear sites last June and the US military's seizure of Venezuela's president in January did not lead to US fatalities.
In a video address, Trump lamented the deaths but added that "sadly, there will likely be more before it ends".
"But America will avenge their deaths and deliver the most punishing blow to the terrorists who have waged war against, basically, civilization," he said.
Michael Waltz, the US envoy to the United Nations, said in a post on X: "Freedom is never free."
A day after the killing of Supreme Leader Ali Khamenei pitched the Middle East and the global economy into deepening uncertainty, the US and Israel pressed ahead with a military campaign that has sent shockwaves through sectors from shipping to air travel to oil.
Trump said the strikes could go on for four weeks.
"It's a big country, it'll take four weeks - or less," Trump told the Daily Mail.
Iran's foreign minister said in a post on X that his country's military had studied "defeats of the US military to our immediate east and west", referring to Afghanistan and Iraq.
"We've incorporated lessons accordingly," he said.
"Bombings in our capital have no impact on our ability to conduct war."
A Reuters/Ipsos poll that concluded on Sunday showed 27 per cent of Americans approved of the strikes, while 43 per cent of the respondents disapproved and 29 per cent were not sure.
Iranian President Masoud Pezeshkian said a leadership council composed of himself, the head of the judiciary and a member of the powerful Guardian Council had temporarily assumed the duties of supreme leader following the killing of Khamenei.
Trump called on Iranians to topple their government, but told the Atlantic magazine that Iran's new leadership wanted to talk.
"They want to talk, and I have agreed to talk, so I will be talking to them. They should have done it sooner ... They waited too long," Trump said.
