State television reported on Wednesday that a tanker carrying tar crashed into the passenger bus in Sanandaj, a city in Iran’s Kurdistan province some 400 km west of Tehran.
Authorities say the tanker ran into the bus just after it left a bus terminal in the city. Both vehicles burst into flames.
Police say the tanker’s brakes failed, causing it to slam into the bus.
Official say at least nine people were injured in the crash.
Kurdistan province has declared three days of public mourning over the crash.
UNICEF says Iran’s rate of traffic crashes is 20 times the world’s average, as the country suffers from poor roads and lax traffic enforcement.