Iranian political prisoner Amir Heshmat Saran has died at the Rajayi Hospital in the city of Karaj, RFE/RL's Radio Farda reports.
Saran's sister and lawyer told Radio Farda that he felt bad on March 4 and was transferred from prison to the hospital the next day.
Saran, who was in his early 50s, reportedly suffered from a heart problem. His lawyer, Mohammad Reza Faghihi, told Radio Farda that he didn't get proper medical care in jail.
The leader of the National Union Front, Saran, was arrested five years ago and sentenced to eight years in prison for creating the small group. He also had to serve eight years after being convicted of calling for illegal gatherings.
Saran's sister said the family considers his death "suspicious" and wants it investigated. There have been several deaths in Iranian prisons in recent years that activists have called suspicious.