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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At least eight people were injured after Qatar was targeted by 44 missiles and 8 drones so far during Iranian attacks, a diplomat briefed on the attacks told ABC News.
-ABC News' Dada Jovanovic
At least four large oil tankers have turned around before passing through the Strait of Hormuz after reports of a warning by Iran that ships should not pass through the strait, according to the shipping data firm Kpler.
The four very large crude carriers - identified as the Orbiter, Universal Victor, Mitake, and Trikwong Venture - represent a combined capacity of some eight million barrels and were set to collect cargoes of oil from ports in Saudi Arabia, Oman and Qatar in the coming days, according to Kpler.
-ABC News' Christopher Looft
The U.S. and partners began the joint attack on Iran at 1:15 am ET to "dismantle the Iranian regime's security apparatus, prioritizing locations that posed an imminent threat," U.S. Central Command (CENTCOM) said in its first statement since the attacks on Iran began.
The attack targets include "Islamic Revolutionary Guard Corps command and control facilities, Iranian air defense capabilities, missile and drone launch sites, and military airfields," CENTCOM said in its statement.
"The President ordered bold action, and our brave Soldiers, Sailors, Airmen, Marines, Guardians, and Coast Guardsmen are answering the call," CENTCOM Commander Admiral Brad Cooper said in the statement.
"There have been no reports of American fatalities or combat-related injuries," and "damage to U.S. installations was minimal and has not impacted operations," according to CENTCOM.
Residents near an industrial complex in Isfahan, Iran, are being warned about an attack on military infrastructure "in a few minutes," the Israel Defense Forces warned in a post on X Saturday.
Residents are being told to evacuate the area "immediately."
