At least 87 people died when a US submarine torpedoed an Iranian warship in the Indian Ocean off Sri Lanka, news agency AFP reported. Rescue operations are still underway as dozens of sailors remain missing after the attack.

The warship, IRIS Dena, a Moudge-class frigate of the Iranian Navy, had recently taken part in the multinational naval exercise MILAN 2026 in India before the incident occurred.

Warship had recently participated in MILAN exercise

IRIS Dena had arrived in India earlier to participate in MILAN, one of the largest multilateral naval exercises in the Indo-Pacific region. The exercise brings together navies from several countries to improve coordination in maritime operations and strengthen regional security cooperation.

According to the Indian Navy, the harbour and sea phases of MILAN 2026 focused on complex operations such as anti-submarine warfare, air defence drills and search and rescue missions.

After completing the exercise, the Iranian frigate had begun its return journey when it was struck by a torpedo fired from a US submarine in international waters.

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US confirms submarine strike

While the US has not confirmed the number of casualties, Defence Secretary Pete Hegseth confirmed that an American submarine carried out the attack.

"An American submarine sank an Iranian warship that thought it was safe in international waters. Instead, it was sunk by a torpedo," Hegseth told reporters.

He described the strike as a demonstration of US military capability during the ongoing conflict with Iran.

The US Department of War also released black-and-white footage that appears to show a submarine periscope view followed by a distant explosion. Military observers noted that it is rare for armed forces to release visuals of submarine attacks so soon after they occur.

Search continues for missing sailors

As per a report by NDTV, a Sri Lankan Navy official said that the rescue teams have recovered 87 bodies so far and are continuing search operations in the waters where the frigate sank.

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Officials said 32 survivors have been rescued, while 61 sailors remain missing, according to Sri Lankan police and navy sources.

Defence analysts said it is unclear whether the US submarine had been tracking the Iranian vessel during its voyage to and from the MILAN exercise. Navies often monitor foreign ships during deployments for intelligence purposes.

Calling the strike a "quiet death", Hegseth said it was the first instance since World War II of the US sinking an enemy ship with a torpedo. "Like in that war," he said, "we are fighting to win."

The strike comes amid the expanding US-Israeli military campaign against Iran. According to the Pentagon, one of the stated objectives of the operation is to target Iran’s naval capabilities.