Fathi said the accident happened around 8 a.m. near the Dehkadeh Sibland complex. He said rescue teams were immediately sent to the site and that the number of victims could rise.
The road links Tehran to Mazandaran province through mountain passes and is one of the busiest intercity routes in northern Iran.
Police road chief Ahmad Karami Asad said the Scania bus, carrying 33 passengers from Qazvin to Mazandaran, overturned in the Aminabad area. He said preliminary checks suggested the driver had been tired and drowsy.
Emergency officials said two of the injured were taken to Imam Khomeini hospital in Firouzkouh, three to Som’e Shaban hospital in Damavand and three were flown by helicopter to Tehran. Other passengers were treated on site. Several of the wounded were reported to be in critical condition.
IRGC-affiliated Tasnim news agency said some passengers were trapped inside the bus before being freed by rescuers.
Road crashes have become a major public concern in Iran. The Legal Medicine Organization said in May that nearly 19,500 people died in traffic accidents in the last Iranian year, most of them on intercity highways. Official data show more than 20,000 deaths were recorded the year before, the highest toll in 12 years.
At least 26 students have died in 13 accidents involving university buses across Iran over the past decade, the daily Ham-Mihan reported this week, reviving concerns about road safety and vehicle standards.