A massive explosion at a port in southern Iran on Saturday killed at least 14 people and injured more than 700, according to state media, and touched off a major fire at the country’s most important import hub.

A person with ties to Iran’s Islamic Revolutionary Guard Corps said that what exploded was sodium perchlorate, a major ingredient in solid fuel for missiles. The person spoke on condition of anonymity to discuss security matters.

The state-run Islamic Republic News Agency quoted an official as saying the explosion was likely set off by containers of chemicals, but did not identify the chemicals. What caused them to detonate was not clear, but the Iranian authorities did not suggest it was sabotage or a deliberate attack.

The security firm Ambrey told The Associated Press that there were indications that the blast resulted from improper storage of sodium perchlorate at the port. The Financial Times reported in January that China had shipped the chemical to Iran, whose stocks of missile propellant were depleted last year when it and its proxy, Hezbollah, launched missiles at Israel.

The explosion and fire sent up immense clouds of black smoke, according to footage from the scene distributed by an Iranian broadcaster and video from social media that was verified by The New York Times. State media broadcasts showed the fire still spreading through the sprawling port complex on Saturday night, several hours after the initial explosion.

The port is Iran’s largest, and last year it handled 85 percent of the country’s shipping container traffic, as well as a large portion of its oil, according to the Port and Maritime Organization.

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