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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Bahrain's Interior Ministry released a statement saying one person was killed and two others were injured after a fire broke out on a foreign ship in Salman Industrial City, as a result of falling debris from an intercepted missile.
Officials said the fire has been brought under control and extinguished.
-ABC News' Will Gretsky
The U.S. has released a joint statement with governments of Bahrain, Jordan, Kuwait, Qatar, Saudi Arabia and the UAE -- all countries impacted by retaliation from Iran over the weekend -- to say they "strongly condemn" the regime's "indiscriminate and reckless missile and drone attacks" on countries across the region.
"The Islamic Republic's actions represent a dangerous escalation that violates the sovereignty of multiple states and threatens regional stability," the statement reads. "The targeting of civilians and of countries not engaged in hostilities is reckless and destabilizing behavior."
-ABC News' Shannon Kingston
The Kuwaiti Air Defense Force has intercepted "a number of hostile aerial targets" on Monday, a spokesperson for the ministry said in a statement.
The missiles targeted the central part of the country, with no casualties recorded, the statement said.
The Israel Defense Forces said it has launched strikes targeting Hezbollah in various parts of Lebanon.
The announcement comes after the IDF had said earlier on Monday that Lebanon had launched projectiles toward northern Israel that were intercepted.
