“Frigate Dena, a guest of India’s Navy carrying almost 130 sailors, was struck in international waters without warning,” he wrote in a post on X early on Thursday.
“Mark my words: The US will come to bitterly regret precedent it has set.”
A Sri Lankan navy spokesman said some 180 people were believed to have been aboard the Iris Dena, based on the ship’s documentation.
The survivors were “seriously injured” and had been taken to a hospital in the southern port of Galle, Sri Lankan Foreign Minister Vijitha Herath said.
Hegseth told a news conference on Wednesday that a US submarine had sunk an Iranian warship “that thought it was safe in international waters”.
He also claimed it was “the first sinking of an enemy ship by a torpedo since World War Two”.
While it is the first time since 1945 that an American submarine has sunk an enemy ship this way, the UK and Pakistan have both sunk vessels using torpedoes since then.
Video released by the US Department of Defense showed a ship being struck, causing the stern to rise up before exploding.
Earlier, Sri Lankan navy spokesman Budhika Sampath had rejected reports that the Iris Dena had been attacked by a submarine.
He added that, at the time rescue operations were launched, rescuers had not seen the vessel – nor any other ships in the region – but saw oil patches and life rafts floating on the water.
Though the ship’s location “was beyond our waters”, Sampath said, “it was within our search and rescue region. So we were obliged to respond as per international obligations”.
