An Iranian detained protester has died days after being freed – the latest death in suspicious circumstances of released activists.

Amir Hossein Tarval Iman was pardoned and released last week after eight months detention but suffered a fatal heart attack a few days later.

His lawyer Maryam Kian Ersi confirmed the death in a tweet on Wednesday.

The "Committee to Follow Up on the Status of Detainees" had announced in a report that Tarval was arrested on October 24, when regime agents raided his home in Aliabad district of Tehran. The report added that he was interrogated and tortured during the detention.

He was tried on a charge of "Moharebeh" or war against God on December 20, facing a possible death penalty.

The committee said Tarval was temporarily released from the notorious Evin prison on bail but died "suspiciously" only ten days later on May 16.

Since protests began last year, regime agents have arrested nearly 20,000 Iranians. Many have been released but a number have died apparently with no certain reason.

19-year-old Yalda Aghafazli died last month after being released from prison without any medical preconditions. Hospital tests indicated a significant amount of narcotics in her blood system.

In November, Arshia Emamgholizadeh, 16, was arrested in East Azarbaijan province for throwing the turban of a cleric. He was kept in prison for ten days and released on bail. He committed suicide two days later. He had told his friends that prison authorities gave them some pills to swallow every night, as well as torturing them.

Some doctors believe that whatever drug was given to some prisoners addicted them to a degree that after being released they experienced severe depression.