As Iran retaliates, largest US military base in Middle East hit by ballistic missile, Qatar says

Gen. Dan Caine, the chairman of the Joint Chiefs of Staff, did not specify a timeline, but said, "This is not a single overnight operation. The military objectives … will take some time to achieve.”

Four U.S. service members have died. Defense Secretary Pete Hegseth told reporters that occurred when Iran hit a tactical operations center that had been fortified. Sources told ABC News that President Donald Trump had been warned ahead of the operation that U.S. casualties were very possible in an operation of this scale.

“We expect to take additional losses,” Caine warned, “and as always, we will work to minimize U.S. losses. But as the secretary said, this is major combat operations.”

Hegseth also noted that “an effort of this scope will include casualties.”

“War is hell and always will be. A grateful nation honors the four Americans we have lost thus far and those injured,” he said.

Hegseth did not rule out troops on the ground.

Caine said that additional American forces, specifically tactical aviation, are headed into the region.

The secretary of Iran's Supreme National Security Council, Ali Larijani, said that Iran is prepared for a long war.

"Iran, unlike the United States, has prepared itself for a long war," Larijani wrote in a post on X on Monday. He added that Iranian armed forces "have not engaged in any attacks except in defense."

Earlier on Monday, Larijani said the Islamic Republic will not negotiate with the U.S.

Defense Secretary Pete Hegseth said “the mission of Operation Epic Fury is laser-focused: destroy Iranian offensive missiles, destroy Iranian missile production, destroy their Navy and other security infrastructure, and they will never have nuclear weapons.”

Gen. Dan Caine, the chairman of the Joint Chiefs of Staff, said there were more than 1,000 targets in the first 24 hours.

“With every passing day, our capabilities get stronger and Iran’s get weaker,” Hegseth said. “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.”

"This is not Iraq, this is not endless," Hegseth said. "... [Trump] called the last 20 years of nation-building wars dumb, and he's right. This is the opposite. This operation is a clear, devastating, decisive mission: destroy the missile threat, destroy the Navy, no nukes."

Defense Secretary Pete Hegseth called the ongoing operation “our retribution” for Iran’s role in sponsoring terrorism, including roadside bombs used against troops during the Iraq War.

Iran’s “war on Americans has become our retribution against their Ayatollah and his death cult,” he said. “It took the 47th president, a fighter who always puts America first, to finally draw the line after 47 years of Iranian belligerence.”

Hegseth said, “This is not a so-called ‘regime change’ war, but the regime sure did change, and the world is better off for it.”