The Iranian Army says a missile strike on a support naval vessel taking part in an exercise in the Gulf of Oman has killed 19 sailors and wounded 15.
The statement drastically raised the death toll the incident, which happened on Sunday.
Earlier Iranian state media reports said the Konarak, a Hendijan-class support ship, was too close to a target during an exercise.
The vessel had been putting targets out for other ships to target, but the missile struck the vessel accidentally, the country's state media said.
Initial reports claimed at least one had been killed.
A local hospital admitted 12 sailors and treated another three with slight wounds, the state-run IRNA news agency reported earlier.
Iranian media said the Konarak had been overhauled in 2018 and was able to launch sea and anti-ship missiles.
The Dutch-made, 47-metre (155-foot) vessel was in service since 1988 and had a capacity of 40 tonnes. It usually carries a crew of 20 sailors.
Iran regularly holds exercises in the region, which is closed to the strategic Strait of Hormuz, the narrow mouth of the Persian Gulf, through which 20% of the world’s oil passes.
The US Navy’s 5th Fleet, which monitors the region, did not immediately respond to a request for comment.
Iranian media rarely report on mishaps during its exercises, signalling the severity of the incident.
This incident also comes amid months of heightened tensions between Iran and the US, after President Donald Trump unilaterally withdrew from Tehran's nuclear deal and imposed crushing sanctions on the country.