The Iranian president has traveled to the coastal province of Hormozgan to get the latest information in person about the rescue and relief efforts at Shahid Rajaei Port following the huge blast.
The president had already called for a probe into the incident and dispatched Interior Minister Eskandar Momeni to the disaster site.
The death toll from the explosion has risen to 25, while over 800 people have been injured.
The Iranian administration declared a public day of mourning on Monday and expressed solidarity with the families of the victims.
The office of the governor of Hormozgan Province released a video that indicates the first moments of a fire before the huge blast.
The CCTV video shows that a fire broke out at the storage site of containers at 12:05 pm local time on April 26. The fire began to rage after a minute and was followed by the catastrophic explosion.
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The provincial governor, Mohammad Ashouri, said weak safety and incompatibility of materials caused the fire to spread to the surrounding containers.
The Crisis Management Organization of Iran said 80 percent of the inferno at the port has been extinguished, noting that the remaining 20 percent will be contained by Sunday night.
Many foreign countries have expressed sympathy with Iran and President of Russia Vladimir Putin on Sunday issued an order to dispatch experts from the Ministry of Civil Defense, Emergencies and Disaster Relief of the Russian Federation to Iran.
The Russian embassy in Tehran said the rescue teams include highly skilled experts who are expected to assist in extinguishing the fire at Shahid Rajaei Port.