Nineteen sailors were killed and another 15 injured in an accident involving Iranian vessels in the Gulf of Oman, the Iranian navy said.
Iranian media reported that the support vessel Konarak was hit by a new anti-ship missile being tested by the frigate Jamaran during an exercise on Sunday.
Konarak was placing targets in the water and remained very close to one, according to reports.
The navy said the ship had been towed ashore and that an investigation had begun.
The incident occurred near the Strait of Hormuz, a strategically important waterway through which about a fifth of the world's oil passes.
"On Sunday night … during naval exercises carried out by various naval force vessels in the waters of Jask and Chabahar, an accident occurred involving the light support vessel Konarak, causing the martyrdom of several courageous members of the ship. Forces," he said. the navy in a statement on Monday.
The statement added that Konarak had been taken to a port for "technical inspection", but made no reference to the circumstances of the accident.
The Iranian armed forces are no stranger to error.
Last January, an air defense unit fired two surface-to-air missiles at an unidentified target, shooting down a Ukrainian plane and killing everyone on board. This error came at a time of heightened tension, with Iranians expecting a U.S. rocket attack in retaliation.
But Sunday's incident occurred in very different circumstances – a planned naval exercise – and raises all sorts of questions about command and control and the professionalism of the Iranian navy.
Iran is trying to expand the scope of its naval operations and improve the armament of its warships. The Jamaran frigate is part of a new class of homemade vessels designed to set a new course for the Iranian navy.
But it remains, to some extent, a neglected service. It is the flotilla of Revolutionary Guard fast patrol boats that appears to be most prominent in Iran's efforts to harass and monitor American ships and other ships in the Gulf.
Iranian media previously reported that Konarak had been accidentally hit by an anti-ship missile fired by the Jamaican during an exercise near the port of Jask.
"The ship was hit after moving a practice target to its destination and not creating enough distance between it and the target," state television said on its website.
Tasnim news agency tweeted in English that Konarak had sunk in the incident. He later reported that the ship was heavily damaged.
It was not clear how many sailors were on board at the time.
The Konarak is a 47 meter long Hendijan class logistical support vessel, manufactured in the Netherlands and purchased by Iran before the 1979 Islamic Revolution.