At least seven boats caught fire at a shipyard in the port of Bushehr in southern Iran, state media reported.
The head of the local crisis management organization told the Irna news agency that the fire had been brought under control and that no casualties had been reported.
The cause was not clear, but it is the latest in a series of mysterious incidents in Iran in recent weeks.
They included explosions and fires in a missile facility, a power plant, a medical clinic and a nuclear complex.
The incidents led to speculation about a sabotage campaign.
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On Monday, a fire broke out in an industrial area near the city of Mashhad in the northeast of the country. According to officials, six gas storage tanks caught fire and it exploded.
The day before, a fire broke out in a petrochemical plant in the southwest of the Mahshahr region, due to an oil leak.
And on Saturday, several bottles of gas exploded inside the basement of a building in Tehran, said the fire department of the capital.
Iranian officials have said they are investigating whether sabotage by foreign powers or national opposition groups could have caused previous explosions at the Natanz uranium enrichment plant on 2 July and at the Khojir missile production facility on June 26.
In 2010, a computer virus widely believed to have been developed by the United States and Israel was used to attack machines in Natanz.