The explosion at Bandar Abbas occurred as Iran began a third round of nuclear talks with the United States in Oman, but there was no indication of a link between the two events.
Hossein Zafari, a spokesperson for Iran's crisis management organisation, appeared to blame the explosion on poor storage of chemicals in containers at Shahid Rajaee.
"The cause of the explosion was the chemicals inside the containers," he told Iran's ILNA news agency.
"Previously, the Director General of Crisis Management had given warnings to this port during their visits and had pointed out the possibility of danger," Zafari said.
However, an Iranian government spokesperson said that although chemicals had likely caused Saturday's blast, it was not yet possible to determine the exact reason.
Iranian President Masoud Pezeshkian ordered an investigation and sent to the site his interior minister, who said efforts were continuing to extinguish the fire and prevent it from spreading to other areas.
Iran's official news channels aired footage of a vast black and orange cloud of smoke billowing up above the port in the aftermath of the blast, and an office building with its doors blown off and papers and debris strewn around.
Located near the strategic Strait of Hormoz, the section of the port affected - Shahid Rajaee - is Iran's biggest container hub, handling a majority of the country's container goods, according to state media.
The blast shattered windows within a radius of several kilometres and was heard in Qeshm, an island 26 kilometres south of the port, Iranian media said.
The semi-official Tasnim news agency posted footage of injured men lying on the road being tended to amid scenes of confusion.
State TV earlier reported that poor handling of flammable materials was a "contributing factor" to the explosion. A local crisis management official told state TV that the blast took place after several containers stored at the port exploded.
A series of deadly incidents has hit Iranian energy and industrial infrastructure in recent years, with many, like Saturday's blast, blamed on negligence.
Iran has blamed some other incidents on its arch-foe Israel, which has carried out attacks on Iranian soil targeting Iran's nuclear program in recent years and in 2024 bombed the country's air defences.
Tehran said Israel was behind a February 2024 attack on Iranian gas pipelines, while in 2020, computers at Shahid Rajaee were hit by a cyberattack.
The Washington Post reported that Israel appeared to be behind that incident as retaliation for an earlier Iranian cyberattack.
Israel has indicated it is nervous about the outcome of US-Iran talks, demanding a full dismantlement of Iran's nuclear program.
There was no immediate comment from Israel's military or Prime Minister Benjamin Netanyahu's office when asked for comment on whether Israel was in any way involved in Saturday's explosion.
Oil facilities were not affected by the blast, Iranian authorities said.
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