The news, which could have serious political ramifications in Washington, came as President Donald Trump emphasized successes in the operation, announcing that nine Iranian naval ships had been sunk and not referring to the US deaths.

The United States and Israel launched massive bombardments against Iran and killed its supreme leader Saturday, with attacks ongoing Sunday.

There was no indication from officials about how or exactly where the American casualties occurred.

"Three U.S. service members have been killed in action and five are seriously wounded as part of Operation Epic Fury. Several others sustained minor shrapnel injuries and concussions -- and are in the process of being returned to duty," US Central Command (CENTCOM) said in a statement.

"Major combat operations continue and our response effort is ongoing. The situation is fluid, so out of respect for the families, we will withhold additional information, including the identities of our fallen warriors, until 24 hours after next of kin have been notified."

Trump, spending the weekend at his Florida resort, gave multiple interviews to US media outlets about other aspects of the Iran operation that were published shortly before the casualties were made public.

He told Fox News that 48 Iranian leaders had been killed "in one shot" and told The Atlantic that he was ready to open negotiations but "can't tell" when.

"Things are evolving in a very positive way right now, a very positive way," he said in another interview with CNBC.

Well after the news broke about the US losses, Trump posted on his Truth Social platform that Iran's navy was being targeted -- but again avoided mentioning the casualties.

"We have destroyed and sunk 9 Iranian Naval Ships, some of them relatively large and important," Trump posted. The country's naval headquarters, he said, was "largely destroyed."

- 'Reckless' war accusation -

The only senior Trump administration official to react initially to the news of US casualties was the ambassador to the United Nations, Mike Waltz, who posted simply: "Freedom is never free."

Hakeem Jeffries, the leader of the Democrats in the House of Representatives, which is controlled by Trump's Republican Party, posted that he was "heartbroken" over the fatalities.

"No more American heroes need to die because of a reckless decision to go to war. Congress must act this week to restrain this president," Jeffries said.

US air and naval forces -- together with Israel's military -- are heavily bombarding Iran, and Trump has said the goal is to destroy the country's military capacity.

In response, Iran has fired missiles at targets in Israel and at US military facilities around the region.

Earlier Sunday, Iran's Revolutionary Guards said they had successfully struck the aircraft carrier USS Abraham Lincoln in the Gulf with four ballistic missiles.

However, CENTCOM said the vessel "was not hit."

"The missiles launched didn't even come close. The Lincoln continues to launch aircraft in support of CENTCOM's relentless campaign to defend the American people by eliminating threats from the Iranian regime," a statement said.

CENTCOM said US forces had sunk an Iranian Jamaran-class corvette warship at a dock in the Gulf of Oman.

The military also announced that B-2 stealth bombers carrying 2,000-pound bombs had been used against "Iran's hardened ballistic missile facilities."