Three staffers in Iran's defense industries have been killed in an explosion in a submarine under construction in the country's south, Iranian state media reported on Saturday.
A report by the Fardanews website said the three technicians were killed when batteries on the vessel exploded.
The explosion took place at a ship-building factory about 37 kilometers (23 miles) west of the southern port of Bandar Abbas that overlooks the Strait of Hormuz.
Since 1992, Iran has developed a homegrown defense industry that produces light and heavy weapons ranging from mortars and torpedoes to tanks and submarines.
In February, President Hassan Rohani unveiled the first Iranian made semi-heavy submarine, saying it was capable of being fitted with cruise missile.
The submarine, named, Fateh has subsurface-to-surface missiles with a range of about 2,000 kilometers (1,250 miles), capable of reaching Israel and U.S. military bases in the region.
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Later that month, Iran successfully tested a cruise missile during naval exercises near the Strait of Hormuz, according to Iran's state media.
"On the third day of the ... exercises, a Ghadir-class Iranian navy submarine successfully launched a cruise missile," the official news agency IRNA reported.
Iran's other submarines, the Tareq and the Fateh, have the same anti-ship capability, IRNA quoted a military statement as saying.
More than 100 vessels were taking part in the ongoing three-day war games in a vast area stretching from the Strait of Hormuz to the Indian Ocean, state media reported.
Iran's expansion of its missile program, particularly its ballistic missiles, has been met with expressions of concern by the United States and European countries. Tehran says the program provides deterrent capabilities and is defensive.