The Iranian army says a missile strike on a naval vessel taking part in an exercise in the Gulf of Oman has killed 19 sailors and wounded 15.

The statement Monday drastically raised the death toll in the incident Sunday.

Earlier Iranian state media reports said the Konarak, a Hendijan-class support ship, was too close to a target during an exercise on Sunday. The vessel had been putting targets out for other ships to target. It said the missile struck the vessel accidentally.

An Iranian missile fired during a training exercise in the Gulf of Oman struck a support vessel near its target, killing at least one sailor and wounding 15 others, Iranian media reported Monday, amid heightened tensions between Tehran and the US.

The friendly fire incident happened on Sunday near the port of Jask, some 1,270 kilometers (790 miles) southeast of Tehran, in the Gulf of Oman, state TV said.

The missile struck the Konarak, a Hendijan-class support ship, taking part in the exercise.

State television described the missile strike as an accident, saying the Konarak had remained too close to the target. The Konarak had been putting targets out in the water for other ships to fire upon, it said.

A local hospital admitted 12 sailors and treated another three with slight wounds, the state-run IRNA news agency reported.

Iranian media said the Konarak had been overhauled in 2018 and was able to launch sea and anti-ship missiles. The Dutch-made, 47-meter (155-foot) vessel was in service since 1988 and had capacity of 40 tons. 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 U.S. Navy’s 5th Fleet, which monitors the region, did not immediately respond to a request for comment.