Sgt. Benjamin N. Pennington, 26, was killed in Saudi Arabia.
President Donald Trump announced "major combat operations" against Iran on Feb. 28, with massive joint U.S.-Israel strikes attack targeting military and government sites, officials said.
Iranian state television confirmed that Ayatollah Ali Khamenei was among those killed in Tehran on the first day of strikes. His son Mojtaba Khamenei was chosen on Sunday to succeed him.
Iran is responding to the operation with missile and drone attacks targeting Israel, regional U.S. bases and multiple Gulf nations. Israel is also intensifying its long-running strike campaign against the Iran-backed Hezbollah militia in Lebanon.
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The U.S. Embassy in Kuwait was "targeted" by Iran, Kuwait's Foreign Ministry said Tuesday in a post to X.
The ministry said it "expresses the state of Kuwait's rejection and condemnation in the strongest terms of the treacherous Iranian attack."
-ABC News' Othon Leyva
The Iranian Red Crescent Society said Tuesday that at least 787 people had been killed by U.S.-Israeli strikes in Iran since Saturday, according to the semiofficial ISNA news agency.
-ABC News' Somayeh Malekian and Morgan Winsor
U.S. Central Command -- CENTCOM -- said in a post to X on Tuesday morning that it had "destroyed Islamic Revolutionary Guard Corps command and control facilities, Iranian air defense capabilities, missile and drone launch sites and military airfields."
"We will continue to take decisive action against imminent threats posed by the Iranian regime," CENTCOM added.
The U.S. Embassy in Riyadh said in a statement that it will be closed on Tuesday following an attack on the facility by Iranian drone strikes overnight.
The embassy said in an update that a shelter-in-place order remained in effect for Jeddah, Riyadh and Dhahran. It urged Americans throughout Saudi Arabia to stay inside.
Tens of thousands of Americans live in Saudi Arabia, according to recent estimates.
-ABC News' Marcus Moore, Dada Jovanovic and Colm O'Molloy
