Paris, Dec 17, 2018 (AFP)

French authorities called on Monday for "light to be shed" on the death of a "blogger and activist" imprisoned in Iran.

The French foreign ministry said in a statement that it had learned "with consternation of the death in detention" of Vahid Sayadi Nasiri, saying he had been imprisoned "for his political activity".

It said he had been on a hunger strike since October 13 to protest "the conditions of his detention and the disregard for his rights".

Iran announced his death on Sunday, but the chief prosecutor of Qom province, Mehdi Kahe, said he had died in hospital of liver disease, according to official news agency IRNA.

It said he had been in prison for "blasphemy", without giving details.

The semi-official ISNA news agency said Sayadi Nasiri died in hospital on December 12.

It said he was arrested in Persian year 1394 (between March 2015 and March 2016) and sentenced to five years for "terrorism" over his membership of a group supporting Iran's monarchy, which was overthrown in the country's 1979 Islamic revolution.

ISNA added that he had been released after 18 months under a pardon by supreme leader Ayatollah Ali Khamenei.

He was rearrested in July after "resuming his work with this terrorist group" including plans for a bomb attack, it said.

France's statement added that the death of Sayadi Nasiri, who was not well-known among activists in Iran, comes at a time of "mounting harassment of human rights defenders in Iran".