Tensions in the US‑Iran war have exploded into the Indian Ocean after a US Navy attack submarine torpedoed and sank an Iranian warship south of Sri Lanka, defence sources say, in the most dramatic naval clash of the conflict so far.

The Virginia‑class submarine had reportedly been tracking the Iranian frigate for hours as it moved along a busy shipping corridor used by Gulf oil tankers heading toward East Asia. When the vessel allegedly switched on fire‑control radar and began closing the distance, US commanders authorised a single heavyweight torpedo shot. Moments later, a violent underwater blast ripped open the frigate’s hull; within ten minutes the ship was listing heavily, smoke pouring from the superstructure, before sliding beneath the waves.

Merchant crews in the area described a “thunderclap from below” and sent Mayday relays as sailors were seen leaping into fuel‑slicked waters. Sri Lanka’s navy scrambled patrol boats and helicopters from Galle, while India diverted a warship and maritime patrol aircraft to join a frantic search‑and‑rescue effort. Dozens of survivors have been pulled from the sea, but many more are feared missing.

Tehran has denounced the strike as “piracy and open war in international waters,” vowing that Iranian missiles and drones will now target US ships “from Hormuz to Sri Lanka.” Washington counters that the frigate was feeding targeting data for earlier Iranian attacks on US forces and insists the engagement was “clear self‑defence under international law.”

With wreckage drifting on one of the world’s most vital sea lanes, regional capitals are asking a chilling question: has the US‑Iran showdown now turned the Indian Ocean itself into a live battlefield?