Of the fatalities 24 passengers died upon impact immediately and four others succumbed to their injuries later in a hospital in Saveh. The incident happened at 03:30 a.m. local time, police announced.
Police have blamed the driver for sleepiness for the tragic incident.
Mohsen Beigi, the national traffic police commander, told the Mehr News Agency that the bus had hit a guardrail and then fell into a 10-meter valley on a solid material.
The bus was moving from the western city of Ilam to Tehran.
Two police officers at the Saveh and Ilam traffic stations have been suspended for inattentiveness. Also Terminal 7 in an Ilam bus station has been suspended from business.
A team of experts was sent to the scene to investigate the degree of each factor involved in such a deadly bus tragedy.
Careless driving is the major cause of accidents in Iran. Unfortunately, police is not tough enough on careless motorists.
PA/AM/SJ
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MNA