MUSCAT, Oman — 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 four people and injuring more than 500 others.

Iranian authorities have said there was a “failure to observe safety principles” at the port of Bandar Abbas, where an explosion Saturday killed dozens of people, but testing is required to determine the causes of the blast.

At least 65 people have died following an explosion at one of Iran's most important ports, according to officials.