A massive fireball lit the sky above the Sina Athar Medical Center in the Iranian capital Tuesday evening after an unexplained explosion was reported at the site of a medical clinic building in northern Tehran's affluent Tajrish Square.
He also said the explosion probably resulted from a gas capsule at the Sina At'har health clinic.
Videos on social media show people gathered outside of the building.
State TV said there could be more explosions because there were a number of oxygen tanks remaining in the medical centre.
Tehran fire department spokesman Jalal Maleki told state TV that the explosion occurred as gas canisters caught fire in the clinic's basement.
Three people were reportedly injured in the blast. "They unfortunately lost their lives due to the heat and thick smoke".
Deputy Health Minister Iraj Harirchi told state TV the clinic had 25 employees at the time of the blast and primarily carries out light surgeries, Reuters reported.
Hossein Ghanzankari tweeted a clip of a person being lifted into an ambulance, commenting: "Iranian news agency says patients are being evacuated from the medical building in north of Tehran after tonight's explosion".
The incident follows an explosion last week near a military site on the outskirts of Tehran that officials blamed on a gas tank.
Iran's state media quoted senior officials as saying the blast was caused by a gas leak.
Parchin is a site suspected of having hosted conventional explosion tests applicable to nuclear power, which the country denies.