Watch Live: Pete Hegseth, Dan Caine hold news conference as Iran airstrikes continue

Defense Secretary Pete Hegseth and Chairman of the Joint Chiefs of Staff Gen. Dan Caine are holding a rare press conference Monday morning as the U.S. and Israeli military operation against Iran continued into a third day.

Hegseth said the mission of the operation, named Operation Epic Fury, is "laser-focused."

"Destroy Iranian missiles, destroy Iranian missile production, destroy their navy and other security infrastructure and they will never have nuclear weapons," Hegseth said.

The Pentagon announced Monday that a fourth American service member has been killed in the mission. The announcement followed the deaths of three U.S. service members in Kuwait over the weekend.

On Monday, Kuwait shot down three U.S. F-15s in what CENTCOM called a "friendly fire incident," but all crewmembers were safe. Smoke rose, meanwhile, from the U.S. Embassy in Kuwait after an apparent Iranian missile strike.

At least 11 people have been killed in Israel. The Iranian Red Crescent says 555 people have been killed in Iran.

President Trump said Sunday that the joint military operation would continue "until all of our objectives are achieved," and that could be "four weeks or less," but that more American casualties are possible.

The U.S. and Israel launched a massive military operation against Iran over the weekend, which included striking Iran's Supreme Leader Ayatollah Ali Khamenei's compound in Tehran and killing him.