Initial reports suggested that the accident happened on a downhill section of the course, and that Golbarnezhan incurred fatal injuries to his neck.
The IPC later issued a statement confirming that the accident occurred on "a mountainous stretch of the course."
They added: "The athlete received treatment at the scene and was in the process of being taken to the athlete hospital when he suffered a cardiac arrest. The ambulance then diverted to the nearby Unimed Rio Hospital in Barra where he passed away soon after arrival."
Sir Philip Craven, president of the IPC, said in a statement: “This is truly heart-breaking news and the thoughts and condolences of the whole Paralympic movement are with Bahman’s family, friends, and teammates as well as the whole of the National Paralympic Committee of Iran. The Paralympic Family is united in grief at this horrendous tragedy which casts a shadow over what have been great Paralympic Games here in Rio.”
The Iranian flag is flying at half-mast in the Paralympic village, and there will be a moment's silence during tomorrow’s closing ceremony.
There will also be an investigation into the circumstances of the accident.
48-year-old Golbarnezhan was born in the Iranian city of Shiraz and made his Paralympic debut in London, when he finished 24th in the road race.
He competed in the time trial earlier this week, finishing 14th.