A U.S. submarine sank an Iranian warship off the southern coast of Sri Lanka, U.S. Defense Secretary Pete Hegseth said on Wednesday, dramatically widening Washington’s pursuit of the Iranian navy.

Sri Lanka’s deputy foreign minister said at least 80 people were killed in the attack on the frigate IRIS Dena, which was heading back to Iran from an eastern Indian port.

“An American submarine sank an Iranian warship that thought it was safe in international waters,” Hegseth said at the Pentagon. “Instead, it was sunk by a torpedo. Quiet death”.

The Iranian vessel had taken part in a naval exercise held in the Bay of Bengal from February 18 to 25, according to the drill’s website.

Sri Lanka Searching for Survivors

Sri Lanka said it had launched a search-and-rescue operation to locate survivors after receiving a distress call, with 32 people rescued by its navy and treated at a hospital in the southern port city of Galle.

Foreign minister Vijitha Herath said 180 people were on board the ship.

Sri Lankan navy spokesman Commander Buddhika Sampath said boats that reached the location observed only an oil slick, adding that the incident took place outside Sri Lankan waters but Colombo was still committed to providing support.

“We are hopeful we can rescue more people and will continue (operations) until we are sure,” Sampath said.

Ship Took Part in Naval Drill Hosted by India

The website of the ‘Milan’ multilateral naval exercise hosted by India listed an Iranian ship named ‘IRINS Dena’ as having taken part in the drill, which was held in the Bay of Bengal off India’s eastern coast.

IRIS – or Islamic Republic of Iran Ship – is the more commonly used prefix for Iranian naval vessels, while IRINS – or Islamic Republic of Iran Naval Ship – is sometimes used.

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(Reporting by Uditha Jayasinghe, Idrees Ali, Phil Stewart, Donia Chiacu and Michelle Nichol; writing by Shilpa Jamkhandikar and YP Rajesh; Editing by Toby Chopra, Jon Boyle and Hugh Lawso)