TEHRAN PROVINCE, Iran — 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 14 people and injuring around 750 others.

Helicopters and aircraft dumped water from the air on the raging fire through the night into Sunday morning at the Shahid Rajaei port. The explosion occurred just as Iran and the United States met Saturday in Oman for the third round of negotiations over Tehran’s rapidly advancing nuclear program.

No one in Iran outright suggested that the explosion came from an attack. However, even Iranian Foreign Minister Abbas Araghchi, who led the talks, on Wednesday acknowledged that “our security services are on high alert given past instances of attempted sabotage and assassination operations designed to provoke a legitimate response.”

State media offered the casualty figures. But there were few details on what sparked the blaze just outside of Bandar Abbas, causing other containers to reportedly explode.

The port took in a shipment of the missile fuel chemical in March, the private security firm Ambrey said. The fuel is part of a shipment of ammonium perchlorate from China by two vessels to Iran first reported in January by the Financial Times. The chemical used to make solid propellant for rockets 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.

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

Ship-tracking data analyzed by The Associated Press put one of the vessels believed to be carrying the chemical in the vicinity in March, as Ambrey said. Iran hasn’t acknowledged taking the shipment. The Iranian mission to the United Nations didn’t respond to a request for comment on Saturday.

It’s unclear why Iran wouldn’t have moved the chemicals from the port, particularly after the Beirut port blast in 2020. That explosion, caused by the ignition of hundreds of tons of highly explosive ammonium nitrate, killed more than 200 people and injured more than 6,000 others. However, Israel did target Iranian missile sites where Tehran uses industrial mixers to create solid fuel.

Social media footage of the explosion on Saturday at Shahid Rajaei saw reddish-hued smoke rising from the fire just before the detonation. That suggests a chemical compound being involved in the blast — like in the Beirut explosion.

“Get back get back! Tell the gas (truck) to go!” a man in one video shouted just before the blast. “Tell him to go, it’s going to blow up! Oh God, this is blowing up! Everybody evacuate! Get back! Get back!”

On Saturday night, the state-run IRNA news agency said that the Customs Administration of Iran blamed a “stockpile of hazardous goods and chemical materials stored in the port area” for the blast, without elaborating.

An aerial shot released by Iranian media after the blast showed fires burning at multiple locations in the port, with authorities later warning about air pollution from chemicals such as ammonia, sulfur dioxide and nitrogen dioxide in the air. Schools and offices in Bandar Abbas will be closed Sunday as well.

Shahid Rajaei has been a target before. A 2020 cyberattack attributed to Israel targeted the port. It came after Israel said that it thwarted a cyberattack targeting its water infrastructure, which it attributed to Iran. Israeli officials didn’t respond to requests for comment regarding Saturday’s explosion.

Social media videos showed black billowing smoke after the blast. Others showed glass blown out of buildings kilometers, or miles, away from the epicenter of the explosion. State media footage showed the injured crowding into at least one hospital, with ambulances arriving as medics rushed one person by on a stretcher.

Hasanzadeh, the provincial disaster management official, earlier told state television that the blast came from containers at Shahid Rajaei port in the city, without elaborating. State television also reported that there had been a building collapse caused by the explosion, though no further details were offered.

The Interior Ministry said that it launched an investigation into the blast. Iranian President Masoud Pezeshkian also offered his condolences for those affected in the blast.

Shahid Rajaei port in Hormozgan province is about 1,050 kilometers (650 miles) southeast of Iran’s capital, Tehran, on the Strait of Hormuz, the narrow mouth of the Persian Gulf through which 20% of all oil traded passes.