The Guardian newspaper in London reported Wednesday it had obtained Amir Hekmati's letter, written recently in Evian Prison in Tehran.
Hekmati, 29, was arrested in 2011 while he was in Iran to visit his grandmother.
"For over two years I have been held on false charges based solely on confessions obtained by force, threats, miserable prison conditions and prolonged periods of solitary confinement," he wrote.
Hekmati's sister Sarah in Flint, Mich., released a statement calling for his release, The Flint Journal reported.
"It's time for him to come home to Michigan, to his family. My brother has committed no crime," the statement said. "More than two years in detention, much of which was spent in solitary confinement, is far too long. He has never been a spy for any country or entity or person. They have punished him enough. We hope Iran's new President [Hassan] Rouhani and his new government recognize this point. We urge his immediate release."
Hekmati was convicted of espionage and sentenced to death. A higher court overturned the sentence on the grounds of weak evidence, but Hekmati has remained incarcerated in Evian, which has a reputation as one of the world's most brutal prisons.
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