Sri Lankan Foreign minister Vijitha Herath had earlier told parliament 180 people were on board the Iranian vessel, which he identified as the IRIS Dena.
A ship named IRINS Dena was listed as taking part in a naval drill held in the Bay of Bengal from February 18 to 25, according to the exercise's website.
Sri Lankan navy spokesman Commander Buddhika Sampath said bodies had been recovered from the sea in the area of the incident.
Thirty-two people were rescued by the Sri Lankan navy and were being treated in hospital in the southern port city of Galle.
The navy received a distress call from an Iranian ship and informed the Sri Lankan air force and both launched a search and rescue operation, he said.
In a Pentagon briefing on Wednesday, Hegseth said that the Tuesday night strike on an Iranian warship was the first such attack on an enemy since World War II.
"An American submarine sunk an Iranian warship that thought it was safe in international waters," Hegseth said.
"Instead, it was sunk by a torpedo."
Rescue boats that reached the site did not see the ship and observed only an oil slick, Sampath said, adding that the incident took place outside Sri Lankan waters but that the country was still committed to providing support.
Sri Lankan forces were focused on saving lives on the Iranian ship and will investigate the cause of the incident later, he said.
Sri Lankan forces had also not observed any other ship or aircraft in the area of the incident, he added.
"We are hopeful we can rescue more people and will continue (operations) until we are sure," Sampath said.
Meanwhile, NATO air and missile defence systems stationed in the eastern Mediterranean destroyed a ballistic missile fired from Iran as it headed into Turkish airspace after passing Syria and Iraq, the Turkish defence ministry says.
The incident marks the first time that NATO member Turkey, Iran's neighbour to the northwest, has been drawn into the expanding conflict between Iran and the United States and Israel that now involves several countries in the region.
"We warn all parties to refrain from actions that would lead to further escalation of conflict in the region. In this context, we will continue to consult with NATO and our other allies," the ministry said, adding there were no casualties or injuries.
"All necessary steps to defend our territory and airspace will be taken resolutely and without hesitation. We remind all parties that we reserve the right to respond to any hostile actions against our country," it added.
Two other initial statements by senior Turkish officials about the incident did not mention NATO's Article 4, which states that allies will "consult together whenever, in the opinion of any of them, the territorial integrity, political independence or security" of a member is threatened.
The missile, which was tracked passing through Iraqi and Syrian airspace, was "neutralised" by NATO systems, Turkish presidency official Burhanettin Duran said in a statement on X.
Turkish officials said debris from the air defence missile that intercepted the ballistic missile fell in the Dortyol district of Hatay province in southeastern Turkey.
with AP and DPA
17°C