Nineteen sailors have been killed and 15 others wounded in a “friendly fire” incident involving two Iranian naval vessels.
Iranian state media reported that a new anti-ship missile being tested by the frigate Jamaran hit the light support ship Konarak on Sunday in the Gulf of Oman.
The accident happened during a training exercise near the Strait of Hormuz.
Iran’s armed forces regularly hold exercises in the strategic waterway.
The Konarak vessel was struck with a missile during a military exercise in the waters of Bandar-e Jask off Iran’s south coast.
“The vessel was hit after moving a practice target to its destination and not creating enough distance between itself and the target,” it added.
The incident happened near the port of Jask, some 1,270km (790 miles) south-east of Tehran, in the Gulf of Oman, state TV said.
The Jamaran and Konarak are said to belong to naval forces of the Iranian military.