Several vessels caught fire on July 15 at Iran’s port of Bushehr on the Persian Gulf, local media reported.
The official IRNA news agency published a photo showing black smoke billowing into the air at a shipyard at the southern port as firefighters battled the blaze.
No casualties were reported, according to the semiofficial Tasnim news agency.
Reports said at least seven vessels were damaged in the fire.
The incident appeared to be the latest in a string of fires and explosions at military and civilian sites across Iran in recent weeks.
Two explosions rocked the capital, Tehran, in late June, one near a military site and the other in a health center, the latter killing 19 people.
A fire also broke out at Iran’s underground Natanz nuclear facility on July 2, officials said.
Iran's top security body said on July 3 that the cause of the Natanz fire had been determined but would be announced at a later time.
Some Iranian officials said it could have been a cyberattack, and one warned that Tehran would retaliate against any country carrying out such attacks.
In an article in early July, state news agency IRNA addressed what it called the possibility of sabotage by enemies such as Israel and the United States, although it stopped short of accusing either directly.
Israel's defense minister said on July 5 his country was not "necessarily" behind every mysterious incident in Iran.