The attack occurred on Wednesday when a U.S. submarine sank the Iranian frigate Dena in the Indian Ocean, about 19 nautical miles off Sri Lanka’s southern port city of Galle, Iranian state media and military sources said.

The incident killed dozens of sailors and marked a dramatic widening of Washington’s military campaign against the Iranian navy beyond the Middle East.

The United States confirmed last week that a U.S. submarine struck the Dena but gave no immediate casualty figures. Washington has characterised the action as part of its ongoing military response to Iranian operations across the region.

Sri Lankan authorities launched search and rescue operations after receiving a distress call from the vessel. Dozens of crew members were rescued by Sri Lankan naval forces, while others remain unaccounted for, according to previous Sri Lankan reports.

Relations between Iran and the United States have deteriorated sharply in recent weeks amid escalating strikes and counter‑strikes across the Middle East, with the naval engagement near Sri Lanka marking one of the most significant confrontations far from the Gulf.