An Iranian warship was accidentally hit by a missile during exercises in the Gulf of Oman, killing at least 19, state television quoted the army as saying, amid tensions with the United States in the waterway.
The friendly fire incident involving the Konarak vessel occurred on Sunday afternoon near Bandar-e Jask, off the southern coast of the Islamic republic, it said on its website.
One report said the vessel had sunk after being hit by a missile fired by another Iranian warship.
"The vessel was hit after moving a practice target to its destination and not creating enough distance between itself and the target," state television said on its website.
Iran's army confirmed the death of 19, saying in a statement that "investigations" were continuing regarding the cause of the incident.
The Konarak is a light logistical support vessel made in the Netherlands and purchased by Iran before the 1979 Islamic revolution.
Weighing 447 tonnes and 47 metres (154 feet) long, the Hendijan-class vessel is equipped with four cruise missiles, according to state television.
It was not immediately clear how many crew members were on board the warship at the time of the accident.
Iran and its arch enemy the US have traded barbs in the past year over a spate of incidents involving their forces in the sensitive Gulf waters.
Tensions have escalated since 2018 when the US withdrew from a multinational accord that froze Iran's nuclear programme and reimposed crippling sanctions on its economy.
Tasnim news agency said in an English-language tweet that the Konarak had sunk after being hit by the missile fired by another Iranian warship.
"Konarak was 'sunk by friendly fire' after Moudge-class frigate 'Jamaran' accidentally shot [it] with a missile during live firing exercise in Jask area of #PersianGulf waters on 10th May."
Tasnim did not mention the detail in its Persian-language report on its website.
Iran's armed forces in January mistakenly shot down a Kiev-bound Boeing 737 passenger jet shortly after takeoff from Tehran, killing all 176 people aboard.
The military admitted to the catastrophic error, saying it came as Iran's air defences were on high alert after firing a barrage of missiles at US troops stationed in Iraq.
Iran launched the missiles in retaliation for the US' killing of its top general Qasem Soleimani in a drone strike days before that.