US Defence Secretary Pete Hegseth has said an American submarine sank an Iranian warship in the Indian Ocean.

He said the ship was sunk by a torpedo on Tuesday and died a "quiet death". He did not name the vessel.

His announcement came after Sri Lanka said its navy had responded to a distress call on Wednesday morning from an Iranian ship named the Iris Dena, which had gone down about 40km (25 miles) from its southern coastline.

Eighty bodies from the frigate were found by rescuers, a Sri Lankan defence official told BBC Sinhala. Another 32 were rescued, the country's navy said.

Iran's Foreign Minister Abbas Araghchi said the US had "perpetrated an atrocity at sea, 2,000 miles away from Iran's shores".

"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".

First launched in 2015, the Iris Dena is a destroyer attached to Iran's Southern Fleet, which is tasked with deployments in the Strait of Hormuz and Gulf of Oman.

It had recently participated in International Fleet Review 2026, a military exercise hosted by India.

The sinking of the Iris Dena comes as the US and Israel have continued to launch air strikes on Iran for a fifth day, with the Israeli military saying it had hit "security headquarters" across the capital, Tehran, on Wednesday.

Israel has also conducted air strikes on Lebanon and has sent ground forces into the south of the country after armed group Hezbollah launched rockets and drones at Israel.

Iran appears to have continued to carry out retaliatory attacks. New strikes were reported in Saudi Arabia and Kuwait on Wednesday, while Turkey said "Nato defences" shot down an Iranian missile heading towards Turkish territory.

Sri Lanka has remained neutral in the conflict. It has refrained from taking any side, calling for "restraint and immediate de-escalation" from "all concerned parties".

Herath, its foreign affairs minister, paid tribute to Iranian Supreme Leader Ayatollah Khameini after he was assassinated on Saturday.

A government spokesman later said Sri Lanka would issue a formal message of condolence regarding all deaths resulting from the conflict, including Iranian state leaders and officials who had been killed.