At least 25 people have been killed and 800 injured in a massive explosion at one of Iran's key ports, authorities say.

The blast took place at Shahid Rajaee, the country's largest commercial port, near the southern city of Bandar Abbas on Saturday morning.

It blew out windows and roofs of nearby buildings and destroyed cars. Residents reported feeling the impact of the blast up to 50km (31 miles) away. Six people remain unaccounted for, state media reports.

Videos verified by the BBC show a fire growing in intensity before a huge explosion, with people subsequently fleeing the blast and others lying wounded on roads surrounded by smoking debris.

"The entire warehouse was filled with smoke, dust and ashes. I don't remember if I went under the table or was thrown there by the blast," one person who was in the area told Iranian state TV.

Aerial footage showed at least three areas ablaze and Iran's interior minister later confirmed that the fire was spreading from one container to another. Schools and offices in the region have been ordered to remain closed on Sunday.

One private maritime risk consultancy said it believed the affected containers had contained solid fuel destined for ballistic missiles.

The fire was the result of "improper handling of a shipment of solid fuel intended for use in Iranian ballistic missiles", Ambrey Intelligence said.

Ambrey added that it was aware that an Iran-flagged ship "discharged a shipment of sodium perchlorate rocket fuel at the port in March 2025".

The Financial Times newspaper had previously reported that two vessels had shipped fuel to Iran from China.

State media quoted witnesses as saying the explosion occurred after a fire broke out and spread to unsealed containers storing "flammable materials".

Customs officials later released a statement reported by Iranian state TV saying the explosion had probably resulted from a fire that had broken out in a hazmat and chemical materials storage depot.

In a later update Ambrey quoted Iran's National Disaster Management Organisation as saying officials had previously issued warnings to Shahid Rajaee port regarding the safe storage of chemicals.

Shahid Rajaee port is Iran's largest and most advanced terminal, through which much of the country's commercial shipping transits.

It is located on the Strait of Hormuz, a major shipping channel for oil cargo, and is about 20km (12 miles) west of Bandar Abbas, Iran's major port city on its south coast and home to the Iranian Navy's main base.

Iran's national oil production company said the explosion at the port had "no connection" to the country's oil refineries, fuel tanks and pipelines, local media reported.

Iranian President Masoud Pezeshkian has expressed his "deep regret and sympathy" for victims. He has announced a government investigation and sent the interior minister to the region to lead it.

Saturday's explosion coincided with the latest round of negotiations between Iranian and US officials on Iran's nuclear programme, with US President Donald Trump aiming to make a deal that would prevent Tehran from gaining nuclear weapons.

Negotiating through Oman mediators, both sides reported that progress had been made, but Iran's top representative said work was still needed to narrow differences. Negotiations will continue next week.

Iran has said it is open to curbs on its nuclear programme in return for sanctions easing but has insisted it will not stop enriching uranium. It insists its nuclear programme is for civilian use.

The talks this year have marked the first high-level engagement between the US and Iran since 2018, when Trump in his first term pulled out of a previous deal to restrict Iran's nuclear activities and reinstated economic sanctions.