Secretary of State John Kerry is calling on Iran to release a former US Marine "unjustly" held for nearly three years.
Amir Hekmati was arrested in August 2011, put on trial and found guilty of spying for the CIA. He was subsequently sentenced to death, a penalty recently overturned and reduced to 10 years in prison.
"Mr Hekmati has spent almost three years in an Iranian prison on false espionage charges. We remain especially concerned about reports of Mr Hekmati's health in prison," Kerry said in a statement on Monday.
"Mr Hekmati's family in the United States has endured the hardship of his absence for too long. He is the eldest son, and his family misses him and needs him home.
"We respectfully request that the government of the Islamic Republic of Iran release Mr Hekmati so that he may be reunited with his family in the United States."
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Hekmati's family and the US government say the dual US-Iranian citizen is not a spy and went to Iran to visit his grandmother.
Supporters and family of the former Marine gathered outside the White House on Monday to demand his release.
Kerry made his request on the Memorial Day holiday in the United States, when the war dead are remembered and military personnel and veterans are honoured.
