A bus carrying students overturned Tuesday on the campus of Islamic Azad University in Tehran, killing at least nine, official IRNA news agency reported.

A total of 27 were injured, Mohammad Karam Dorabadi, public relations manager of Tehran Emergency Center, was quoted as saying.

Four injured students are in critical condition, he added.

Hossein Abedi, acting police chief of Tehran, told IRNA that the cause of the incident is under investigation.