US says Iran’s frigate sunk by submarine was legitimate target, rejects claim it was unarmed

March 9, 2026, by Fatima Bahtić

The United States Indo-Pacific Command (INDOPACOM) has rejected Iran’s claim that the Iranian naval vessel IRIS Dena was unarmed at the time it was targeted, describing the assertion as false.

In a statement, the US command said the vessel constituted a valid military objective and that the strike was conducted in accordance with the principles of the Law of Armed Conflict (LOAC). According to INDOPACOM, the use of force against the Iranian warship was authorized under international law governing armed conflict at sea.

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The command said the operation followed established targeting procedures and legal reviews designed to ensure compliance with LOAC, including the principles of distinction and military necessity. These principles allow the use of force against legitimate military targets while requiring precautions to minimize harm.

The incident occurred on March 4 in international waters off the coast of Galle, when a US Navy submarine struck the Iranian vessel with a torpedo, according to American officials.

The US Secretary of Defense Pete Hegseth revealed in a social media post that a US submarine sank an Iranian warship in the Indian Ocean. He noted that this was the first sinking of a ship by a torpedo since World War II.

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Operations

The attack sank the ship within minutes and triggered a search and rescue operation led by Sri Lankan authorities.

Sri Lankan naval forces recovered dozens of bodies and rescued several survivors from the water after the sinking. At least 87 sailors were reported killed and more than 30 rescued following the attack, according to media outlets.

Iran has strongly disputed the US account. Speaking at the United Nations headquarters in New York, Iran’s ambassador to the UN, Amir‑Saeid Iravani, accused the United States of violating international law.

“The United States committed a dangerous act of aggression at sea,” Iravani said, calling the attack a war crime and a violation of the principle of freedom of navigation.

He said the frigate had been on a goodwill visit and operating with the Indian Navy when it was struck in international waters.

Diplomatic tensions between Washington and Tehran have continued to escalate in the days since the attack, with both sides presenting conflicting narratives about the operations conducted in the region.