Several people were injured at the Sina Athar clinic, and there are fears the death toll will rise further.

Iran's state media quoted senior officials as saying the blast was caused by a gas leak.

Television pictures showed plumes of smoke billowing in the sky. Firefighters extinguished the blaze several hours later.

Most of the victims of Tuesday's blast were women, according to the authorities.

Some of the victims "were in upper floors, in operation rooms - who were either patients being operated on or those with them", Tehran fire department spokesman Jalal Maleki was quoted as saying by state media.