By Selena Hill (staff@latinospost.com) | First Posted: Sep 12, 2013 10:15 AM EDT

A former U.S. Marine detained in Iran for two years addressed a letter to the U.S. Secretary of State John Kerry stating that he has endured "miserable prison conditions" and that he believes Tehran is holding him hostage for use in a prisoner exchange.

Amir Hekmati's smuggled letter was handwritten on Sept. 1 and was first published Wednesday by The Guardian.

The 29-year-old U.S. citizen was detained in Iran in 2011 on what the U.S. says are false espionage charges. He was picked up by Iranian security officials two weeks after arriving in Tehran from Dubai on a family visit. However, Iran accused him of being a CIA spy, then tried, convicted and sentenced him to death. Iran's Supreme Court ordered a retrial last year, but he remains imprisoned.

Hekmati also said that his televised confession was forced and was used to implicate him in trial.

"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," Hekmati wrote in the letter.

John Kerry urged Tehran leaders to release him from prison on the second anniversary of his arrest last month, saying Washington was "deeply concerned" about his detention.

In his letter, Hekmati accuses the Iranian authorities of employing "unlawful tactics" to keep him in prison in hopes of swapping him for Iranian prisoners held in U.S. custody.

"This is part of a propaganda and hostage-taking effort by Iranian intelligence to secure the release of Iranians abroad being held on security-related charges," Hekmati says in the letter.

Hekmati's state-appointed Iranian lawyer was told by the authorities that he will be released only if two Iranians held in foreign jails are freed, he writes.

"I had nothing to do with their arrest, committed no crime, and see no reason why the US government should entertain such a ridiculous proposition," he writes, failing to reveal the names of the Iranian prisoners concerned.

Hekmati goes on to urge Kerry not to buckle under the pressure of Iran's demands.

"I do not wish to set a precedent for others that may be unlawfully [obtained] for political gain in the future," he writes, reports The Star.

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