Tehran has accused Washington of committing an “atrocity at sea” after an Iranian naval frigate was sunk by a United States submarine in the Indian Ocean, triggering a sharp escalation in tensions surrounding the widening conflict involving Iran, the United States and Israel.Foreign Minister Seyed Abbas Araghchi issued the condemnation in a statement on the social media platform X, asserting that the warship IRIS Dena had been struck without warning while sailing in international waters thousands of miles from Iranian territory. He described the vessel as a “guest of India’s Navy” and said it carried nearly 130 sailors at the time of the attack. “The US has perpetrated an atrocity at sea,” Araghchi wrote, warning that Washington would “come to bitterly regret the precedent it has set.”
The frigate was torpedoed on 4 March by a United States Navy submarine operating in the Indian Ocean, roughly 40 nautical miles south of the Sri Lankan port city of Galle. Defence officials in Washington confirmed that the attack involved a Mark 48 torpedo fired from a submarine positioned in the area. The engagement sank the 95-metre Moudge-class warship within minutes after a distress call was transmitted.
Casualty figures emerging from rescue operations indicate that at least 87 members of the crew were killed. Sri Lankan naval authorities reported rescuing 32 survivors from the water and transferring them to hospital facilities in Galle for treatment, while dozens of others remain missing. The vessel was believed to have carried about 180 personnel during its voyage through the Indian Ocean.
IRIS Dena had taken part in the multinational naval exercise Milan 2026 and the International Fleet Review held at Visakhapatnam before beginning its return journey toward Iranian waters. The exercises involved warships from several countries and focused on maritime cooperation and security in the Indo-Pacific region. Iranian naval officials had presented the deployment as part of Tehran’s efforts to expand its maritime diplomacy and demonstrate blue-water capabilities beyond the Persian Gulf.
The strike marks one of the most significant naval engagements linked to the expanding confrontation between Iran and a coalition led by Washington and Israel. Military analysts note that submarine torpedo attacks against surface warships have become rare in modern naval warfare. The sinking of IRIS Dena is widely regarded as the first confirmed case of a United States submarine destroying an enemy vessel in combat since the Second World War.
Pentagon officials characterised the attack as a deliberate military action tied to the broader conflict unfolding across the Middle East. Defence Secretary Pete Hegseth acknowledged that a United States submarine had intercepted the Iranian ship and launched the torpedo strike, describing the operation as swift and decisive. American officials argue that the naval engagement formed part of ongoing operations aimed at weakening Iranian military assets during a rapidly intensifying regional confrontation.
Iranian authorities have strongly rejected that justification. Araghchi insisted the frigate posed no immediate threat and had been travelling in international waters far from the central theatre of hostilities. Iranian officials contend the strike represents an unlawful escalation and have urged the international community to condemn what they describe as a dangerous precedent in maritime warfare.
The episode has intensified diplomatic scrutiny across Asia and the Middle East. Sri Lankan authorities found themselves drawn into the crisis after receiving the distress signal from the Iranian vessel shortly before dawn. Search-and-rescue teams from the Sri Lanka Navy and Air Force were deployed to the area and recovered bodies as well as survivors amid debris scattered across the sea surface.
Officials in Colombo emphasised that the incident occurred outside Sri Lankan territorial waters but within the country’s exclusive economic zone. The government has coordinated with Iranian representatives regarding rescue efforts and the treatment of injured sailors while monitoring the broader security implications for shipping routes in the region.
Strategic analysts say the destruction of the frigate highlights the widening geographical scope of the confrontation. Earlier phases of the conflict centred largely on missile exchanges, air strikes and proxy clashes across the Middle East. The naval strike in the Indian Ocean suggests that military operations linked to the dispute may extend far beyond the Gulf and into key international shipping corridors.
Energy markets and global shipping operators have been closely watching the situation. Heightened hostilities have already disrupted maritime traffic through the Strait of Hormuz, one of the world’s most critical oil transit chokepoints. Insurance premiums for vessels moving through parts of the Indian Ocean and Gulf region have risen sharply as naval forces increase their patrols and commercial ships adjust routes to avoid potential conflict zones.
For Tehran, the loss of IRIS Dena carries both military and symbolic significance. Commissioned in 2021 and built at naval facilities in Bandar Abbas, the frigate formed part of Iran’s effort to develop domestically produced surface combatants capable of operating across distant seas. The vessel carried anti-ship missiles, air defence systems and a helicopter platform designed for anti-submarine missions.