A file photo of Iran`s Frigate IRIS Dena

Iran`s Army says 104 personnel on board the Frigate Dena have lost their lives during a "savage" attack by the United States in international waters.

The attack happened hundreds of miles away from the war zone in the Persian Gulf - off the southern coast of Sri Lanka-on Wednesday, the Army said in a statement on Sunday.

Frigate IRIS Dena was torpedoed and sunk by a US submarine. According to Sri Lanka`s deputy foreign minister, it was heading back to Iran from an eastern Indian port.

The Army said the ship was returning home after participating in the "Milan 2026" naval exercise, a multinational maritime drill in India, when the US Navy carried out the attack without any advanced warning and in violation of all humanitarian laws and international maritime regulations.

A total of 136 personnel were on board the frigate, 104 of whom were martyred and 20 others went missing, according to the statement.

Thirty-two sailors were wounded in the attack and were transferred to a hospital in Sri Lanka.

It emphasized that the terrorist US Navy`s inhuman attack, which occurred miles away from the war zone, violated humanitarian rules and international maritime regulations.

Frigate IRIS Dena had taken part in a naval exercise organized by India in the Bay of Bengal from February 18 to 25.

In a post on X on Thursday, Iranian Foreign Minister Abbas Araghchi vowed that the United States will "bitterly regret" sinking Iran`s Frigate Dena.

"The US has 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. Mark my words: The US will come to bitterly regret the precedent it has set," Araghchi wrote.