At least seven ships have caught fire at the Iranian port of Bushehr, the Tasnim news agency reported on Wednesday, in what appeared to be the latest in a series of unexplained incidents around nuclear and industrial installations since late June.
No casualties have been reported, the agency said.
There have been several explosions and fires around Iranian military, nuclear and industrial facilities since late June, including a fire at Iran's underground Natanz nuclear facility on July 2.
Natanz is the centrepiece of Iran's enrichment programme, which Tehran says is for peaceful purposes. Western intelligence agencies and the UN's nuclear watchdog (IAEA) believe it had a coordinated, clandestine nuclear arms programme that it halted in 2003.
Tehran denies ever seeking nuclear weapons.
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 have said it may have been cyber sabotage and one of them 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 defence minister said on July 5 his country was not "necessarily" behind every mysterious incident in Iran.