Tehran’s Deputy Governor General for Security Affairs Mohsen Hamedani told Tasnim that the fire was caused by an electrical malfunction.
He also dismissed the idea that a gas leak was behind the incident or that the cause was security-related.
The fire began on Thursday morning at the Plasco building in in downtown Tehran.
The 17-story structure crumbled after the fire engulfed the top storeys of the building as scores of firefighters battled the blaze.
Tehran Mayor Mohammad Baqer Qalibaf said between 20 to 25 people are believed to have been trapped under the rubble.
Firefighters are now searching to take out their comrades remaining under the rubble.
The high-rise was inaugurated in 1962 and named after a plastics manufacturing company. It was the tallest building in the city at the time of its construction. It included shopping centers and clothing workshops.