Washington DC - Defense Secretary Pete Hegseth on Monday declined to rule out putting US boots on the ground in Iran and indicated the unprovoked war launched over the weekend could go on for as long as six weeks.

US forces began carrying out sweeping strikes on Iran Saturday in concert with Israel, and have struck hundreds of targets across the country since then, including the Islamic republic's missiles, navy, and command-and-control sites.

When asked if the US already troops 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 added. "I think it's one of those fallacies for a long time that this department or presidents or others should tell the American people and our enemies by the way, 'Here's exactly what we'll do, here's exactly how long we'll go.'"

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As for how long the war will last, Hegseth said: "Four weeks, two weeks, six weeks, it could move up. It could move back."

Hegseth sought to differentiate the Iran operation from past US wars in Iraq and Afghanistan, saying the current assault is not an effort to impose a democracy.

"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, hours after US Central Command announced the death of a fourth service member.

"This is not Iraq. This is not endless," Hegseth insisted. "Our generation knows better and so does this president. He called the last 20 years of nation building wars 'dumb' and he's right."

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"With every passing day, our capabilities get stronger and Iran's get weaker. We set the terms of this war from start to finish. Our ambitions are not utopian, they are realistic scoped to our interests and the defense of our people and our allies," he added.

General Dan Caine, chairman of the Joint Chiefs of Staff, spoke alongside Hegseth, saying that air superiority had been achieved over Iran.

US and Israeli strikes have already killed well over 500 people in Iran, according to local authorities. The death toll in the bombing of an elementary girls' school rose to 165 on Sunday.