The Pentagon played down concerns on Monday that the US attack on Iran risked plunging the United States into a new, open-ended conflict in the Middle East, even as officials declined to offer a timeline and cautioned that they expected more US casualties.
The United States and Israel launched their most ambitious attacks on Iran in decades on Saturday, killing Supreme Leader Ayatollah Ali Khamenei, sinking Iranian warships and hitting more than 1,000 targets so far.
In the first Pentagon briefing since the conflict began, US General Dan Caine, the Chairman of the Joint Chiefs of Staff, told reporters it would take time to achieve US military objectives in Iran.
Defense Secretary Pete Hegseth listed those objectives in primarily military terms, saying the Pentagon sought to destroy Iran's navy and expansive missile capabilities that could shield any covert attempts by Tehran to later build a nuclear weapon. Iran denies it wants nuclear weapons.
"To the media outlets and political left screaming 'ENDLESS WARS' - stop. This is not Iraq. This is not endless," said Hegseth, a US Army veteran who served in Iraq from 2005 to 2006 and deployed to Afghanistan in 2012.
Still, Hegseth mocked a reporter who asked about the timeline for the campaign, saying Trump would not be pinned down, even after the US president suggested on Sunday that strikes against Iran could go on for the next four weeks.
The US and Israeli attacks have triggered a massive Iranian retaliatory response but many of the most dangerous drones and missiles have been intercepted by US military forces and US allies in the region.
Still, some of the attacks succeeded in inflicting US losses. The US military said a fourth US service member died on Monday as a result of injuries in the Iran operations.
Six US service members were also injured on Monday when Kuwaiti air defenses shot down their three F-15 fighter jets by mistake.
"We expect to take additional losses," Caine told the briefing, adding the United States would work to minimize US losses but, "this is major combat operations."
As the US-Israeli air war against Iran expanded on Monday, Caine said the US military buildup in the Middle East continued, even after the biggest deployment since the 2003 invasion of Iraq.
"This is not a single overnight operation. The military objectives that Centcom and the Joint Force have been tasked with will take some time to achieve, and in some cases will be difficult and gritty work," Caine told reporters.
Even with the US-Israeli strikes, the conservative clerical leaders in Iran have shown no sign of yielding power. Some military experts say US and Israeli air power, with no armed force on the ground, may not be enough to drive them out.
Hegseth said there were no US troops on the ground. But he also declined to rule that possibility out.
"We are not going into the exercise of (saying) what we will or will not do," Hegseth said. "President Trump ensures that our enemies understand we'll go as far as we need to go to advance American interests."
"But we're not dumb about it. You don't have to roll 200,000 people in there and stay 20 years."
(Reporting by Phil Stewart, Idrees Ali, Doina Chiacu; editing by Susan Heavey, Michelle Nichols and Nick Zieminski)