A French citizen detained in Iran for over two years on espionage charges revealed his identity and described his ordeal in a phone call aired on French radio on Monday, as Paris steps up efforts to gain his release.

In the conversation recorded in prison and aired by radio network France Inter, Olivier Grondeau, who had previously only been identified only by his first name, described his detention as arbitrary and unbearable.

The 34-year-old tourist who was arrested in Shiraz on October 12, 2022 during a world tour added that he is a victim of what he called political blackmail as France and Iran grapple over his case.

Grondeau was sentenced last February to five years in prison for "espionage and conspiracy against the Islamic Republic" and is currently held in Tehran’s Evin Prison in a wing designated for foreign and dual-national detainees.

He called on French authorities to secure his release and expressed hope that his request for parole would be granted.

The French foreign ministry, which summoned Iran’s ambassador on January 10, has demanded the immediate release of Grondeau and two other French detainees, teachers Cécile Kohler and Jacques Paris, who have been held since May 2022.

"Their situation is intolerable, with inhumane detention conditions that, in some cases, constitute torture under international law," the ministry said in a statement.

Grondeau shares a cell with 18 other detainees and has limited access to a library and books sent by the French embassy. He also highlighted the harsher conditions faced by Kohler and Paris in the same message.

"You, who have the power to influence this matter, hear this truth," Grondeau said, apparently addressing French authorities.

"Cecile's strength, Jacques' strength, Olivier's strength, it is all running out," he added.

"Your responsibility is called upon to ensure the survival of three human beings."

Grondeau is one of an unknown number of foreign or dual-nationals held by Iran in what rights groups and some foreign governments decry as hostage diplomacy.

Most recently, an Italian journalist was released in an arrest which is understood to have been leverage to force Italy to release an Iranian imprisoned on terrorism charges.