Iran's interior minister has said negligence was a factor in the massive explosion and fire at the country's largest container port, as the death toll rose to at least 70.

Eskandar Momeni said Saturday's blast at Shahid Rajaee port in Bandar Abbas, which also injured more than 1,000 people, was caused by "shortcomings, including noncompliance with safety precautions and negligence".

"Some individuals deemed responsible" had been summoned for questioning, he added.

Customs authorities have said imported cargo caught fire and exploded. The defence ministry has denied foreign reports that it was a shipment of a missile fuel chemical.

The crisis management director for Hormozgan province, Mehrdad Hassanzadeh, also said on Monday that the firefighting effort at the port was "almost in its final stages".

Hormozgan Governor Mohammad Ashouri Taziani meanwhile said clearing-up operations at the port could continue for several more days, and that it could take one to two weeks before the situation there returned to normal.

He estimated that 1,500 hectares (3,700 acres) - almost two-thirds of the site - were severely affected by the explosion.

The Customs Administration said the cargo which caught fire and exploded had neither been registered nor formally declared before the incident, according to the Isna news agency.

On Sunday, the CEO of the firm that was operating the affected area, Sina Marine and Port Services Development Company, blamed "a repeated and catastrophic error involving false declarations of hazardous goods".

Iran's defence ministry denied reports that the explosion was caused by the improper handling of a shipment of sodium perchlorate, a solid fuel used for ballistic missiles.

Spokesman Brig Gen Reza Talai-Nik said on Sunday that there "were and are no import or export of fuel shipments or cargo for military use in the vicinity of the incident", and accused foreign media of spreading "fake news".

Ambrey Intelligence, a private maritime risk consultancy, told the Associated Press that the port received a shipment of sodium perchlorate last month, and that the blast was "reportedly the result of improper handling".

The New York Times also cited an unnamed person with ties to Iran's Revolutionary Guards as saying that sodium perchlorate exploded.