A loud explosion was heard in northern Tehran on Tuesday evening causing thick clouds of smoke to fill the skies, Iranian News Agency ISNA reported on Tuesday.

According to state media, the blast in question happened in the underground levels of Tehran’s Sina Athar medical clinic and patients are currently still inside the building.

The head of the Tehran Emergency Center, Peyman Saberian, told the Fars news agency that three people have been injured in the fire.

However, several reports on social media have already reported at least 17 dead from the attacks, with dozens more injured.

The explosion was caused by a gas leak, Tehran Deputy Governor Hamid Reza Goudarzi told state TV.

Jalal Maleki, the Tehran Fire Department spokesman, told the Tasnim news agency that a fire had broken out in a medical clinic in north Tehran and firefighters have been sent to the scene.

Last week, an explosion took place close to a sensitive military site near Tehran which a defense ministry spokesman told state TV was caused by a tank leak at a gas storage facility.