Nineteen Iranian sailors were killed and 15 injured on Sunday after a support vessel was hit by a friendly fire missile during naval exercises, off the country’s southern coast, AFP reported on Monday, quoting the state media and the army.

Iran’s Tasnim news agency said the support vessel, named Konark, was hit by the missile fired by another Iranian warship near the port of Jask, 790 miles south-east of Tehran, in the Gulf of Oman. Iran regularly holds military exercises in the region.

It was not immediately clear how many crew members were on board the warship at the time of the accident.

The Islamic republic’s state broadcaster described the missile strike as an accident. “The vessel was hit after moving a practice target to its destination and not creating enough distance between itself and the target,” the channel said, according to The Guardian.

The Konarak is a logistical support vessel made in the Netherlands and purchased by Iran before the 1979 Islamic revolution. It is equipped with four cruise missiles.

The incident came amid months of escalating tensions between Iran and the United States since President Donald Trump withdrew from the country’s nuclear deal with world powers in 2018 and imposed strict sanctions on the country.

The two nations have traded allegations since the last year over incidents involving their forces in the strategic and sensitive Gulf waters. Their latest confrontation came on April 15, when the US claimed that Iranian boats had “harassed” its navy ships in the waterway. After the confrontation, Trump had instructed the US Navy to fire on any Iranian ships that harass it at sea.

In January, Iran’s armed forces shot down a Ukraine-bound Boeing 737 passenger jet shortly after takeoff from Tehran, killing all 176 people aboard.The military admitted to the disastrous error and said that they were on high alert after firing a barrage of missiles at US troops stationed in Iraq, in retaliation for the killing of its top general Qasem Soleimani.