US President Donald Trump said on Monday he had ordered the attack on Iran to thwart Tehran's nuclear development and a ballistic missile program that he said was growing rapidly.
Trump offered his most extensive comments about the war beyond two video messages and a series of brief phone interviews with reporters over the weekend that offered sometimes conflicting objectives in the conflict.
He said, without providing evidence, that the threat from Iran had been imminent.
"This was our last best chance to strike ... and eliminate the intolerable threats posed by this sick and sinister regime," he said at an event in the White House East Room.
Trump said military operations were ahead of schedule, without providing details. He said he had projected the US campaign would last four to five weeks but that it could go longer.
A central premise of the fight was to prevent Iran from developing a nuclear weapon, which Tehran has denied doing, and thwart its long-range ballistic missile program, Trump said.
"An Iranian regime armed with long-range missiles and nuclear weapons would be an intolerable threat to the Middle East, but also to the American people," Trump said.
Trump said US forces had knocked out 10 Iranian ships - "they're at the bottom of the sea" - and expressed confidence about how the campaign was going.
"Today, the United States military continues to carry out large-scale, combat operations in Iran to eliminate the grave threats posed to America by this terrible, terrorist regime," Trump said.
He said the objectives of the war included destroying Iran's missile capabilities, annihilating their navy and stopping from them from having a nuclear weapon.
Trump said a third objective was a long-standing US goal, to prevent Iran from supporting militant groups elsewhere in the region.
Trump noted the loss of four American service personnel in the fight so far, adding: "In their memory, we continue this mission with ferocious, unyielding resolve to crush the threat this terrorist regime poses to the American people."
- Ground troops -
Earlier, Trump said he is not ruling out sending US troops into Iran, while threatening a new, "big wave" of attacks.
The 79-year-old Republican has long campaigned against decades of US military entanglements in the Middle East, but ordered a large-scale war against Iran starting Saturday.
While so far the assault has focused entirely on aerial attacks by missiles and bombs, Trump refused to rule out sending ground troops -- something generally considered to be far riskier in terms of possible casualties.
"I don't have the yips with respect to boots on the ground -- like every president says, 'There will be no boots on the ground.' I don't say it," Trump told the New York Post in one of numerous brief interviews he has given since launching the Iran operation.
"I say 'probably don't need them,' [or] 'if they were necessary,'" he said.
Trump also spoke to CNN on Monday, flagging what he said would be an escalation in the assault on Iran.
"We haven't even started hitting them hard. The big wave hasn't even happened," he told CNN, without elaborating. "The big one is coming soon."
US and Israeli forces have so far struck hundreds of targets across Iran, including the country’s missiles, navy and command-and-control sites.
Four US military members have been announced killed and three fighter jets have been shot down -- officially in friendly fire.
Iran has fired missiles at Israel, at US bases around the region and also at targets in regional Arab countries -- Bahrain, Jordan, Kuwait, Qatar and the United Arab Emirates -- something that Trump called "the biggest surprise."
Trump's comments came shortly after Defense Secretary Pete Hegseth also signaled that deploying troops inside Iran had not been ruled out.
Asked if there were already boots on the ground, Hegseth told a news conference: "No, but we're not going to go into the exercise of what we will or will not do."
"We'll go as far as we need to go," he said.
As for how long the war will last, Hegseth said: "Four weeks, two weeks, six weeks, it could move up. It could move back."
He sought to differentiate the Iran operation from past long-running US wars in Iraq and Afghanistan, saying the war is not an effort to build democracy in Iran.
"No stupid rules of engagement, no nation building quagmire, no democracy-building exercise. No politically correct wars. We fight to win and we don't waste time or lives," the Pentagon chief said.
"This is not Iraq. This is not endless," Hegseth said. "Our generation knows better and so does this president. He called the last 20 years of nation building wars 'dumb' and he's right."
General Dan Caine, the top US military officer, spoke alongside Hegseth, saying that air superiority had been achieved over Iran.
Strikes by American forces "resulted in the establishment of local air superiority. This air superiority will not only enhance the protection of our forces, but also allow them to continue the work over Iran," Caine said.
