Washington DC - A US submarine sank an Iranian warship in the Indian Ocean, Defense Secretary Pete Hegseth said Wednesday, touting the deadly strike as evidence of America's global reach in its war on Iran.

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

Sri Lankan authorities said they had rescued 32 crew members from the frigate IRIS Dena but that 148 other sailors were missing, with hopes low that any more would be found.

Hegseth called the attack "quiet death" and the first US sinking of an enemy ship by torpedo since World War II.

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"Like in that war," he said, "we are fighting to win."

The Pentagon says one of the main aims of the US-Israeli war against Iran, launched Saturday, is to wipe out the country's navy.

Sri Lanka's foreign minister, Vijitha Herath, told parliament that the rescued Iranians were rushed to the main hospital in the island's south while two navy craft and a plane were deployed to search for others.

The frigate issued a distress call at dawn on Wednesday, and within less than an hour, a rescue vessel reached the area about 25 miles south of the southern port of Galle, the minister said.

The frigate had completely sunk, and only an oil patch remained when the navy rescue boats approached.

"We are keeping up a search, but we don't know yet what happened to the rest of the crew," a Sri Lankan defense official told AFP.

Sri Lankan navy spokesman Buddhika Sampath said their operation was in line with Sri Lanka's maritime obligations.

"We responded to the distress call under our international obligations, as this is within our search and rescue area in the Indian Ocean," Sampath told AFP.

"We have found a few bodies from the area where the ship had gone down," Sampath.

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Sri Lanka has remained neutral and repeatedly urged dialogue to resolve the conflict in the Middle East.

Just over a million Sri Lankans are employed in the Middle East, and they are a key source of foreign exchange for the country, emerging from its worst economic meltdown in 2022.

Both Sri Lanka's navy and the air force said they were not releasing footage of the rescue because it involved the military of another state.

Police stepped up security outside the Galle hospital as the wounded Iranians were brought there by the local navy.

The Iranian Ambassador in Colombo, Alireza Delkhosh, was not immediately available for comment.