The bus travelling from Kerman to Tehran skidded off the road near the city of Mehriz, in Yaz Province, at around 10 p.m. (local time) Friday, Head of the Roads Management Center of Kerman Province Mohsen Kashani told the Tasnim News Agency.
The driver of the vehicle died of injuries at a hospital, bringing the death toll to five, the official stated.
Kashani also said that two injured victims are also in critical conditions in the hospital.
Iran has a good road network but accidents caused by reckless drivers kill thousands each year.
According to the figures released by World Atlas in September 2016, Iran is ranked 4th in the list of countries with the highest road traffic death rates.
The estimated road traffic death rate per 100,000 people in Iran was 34.1.