A massive explosion and fire rocked a port Saturday in southern Iran purportedly linked to a shipment of a chemical ingredient used to make missile propellant, killing five people and injuring more than 700 others.

However, the port took in a shipment of “sodium perchlorate rocket fuel” in March, the private security firm Ambrey said. The fuel is part of a shipment from China by two vessels to Iran first reported in January by the Financial Times. The fuel was going to be used to replenish Iran’s missile stocks, which had been depleted by its direct attacks on Israel during the war with Hamas in the Gaza Strip.