In a photograph of the incident released by the official IRNA news agency, thick black smoke plumes billowed into the air. State broadcaster IRIB showed fighters tackling smoke clouds at a shipyard in the southern Gulf harbour.

Several explosions and fires have occurred around Iranian military, nuclear, and industrial installations since late June, including a fire on July 2 at the underground nuclear facility in Natanz, Iran.

Natanz is the cornerstone of Iran's enrichment program, for peaceful purposes, Tehran claims.

Western intelligence services and the IAEA say it had a planned, covert nuclear weapons program that it halted in 2003. Tehran denies nuclear weapons are being tried.

Iran's top security body said on July 3 that it had identified the cause of the Natanz fire but would be revealed at a later date.

State news agency IRNA discussed what it called the threat of interference by rivals like Israel and the United States in an article in early July, but it stopped short of any specifically accusing it.

Israel's defense minister said his country was not "necessary" behind any mysterious incident that took place in Iran on July 5.

Maritime Business World