The father of a US citizen imprisoned in Iran forwarded a letter to President Hassan Rouhani on Wednesday pleading with him to free his son on humanitarian grounds. Ali Hekmati, who is originally from Iran and lives in the US state of Michigan, said he was \"very sick\" with a brain tumor and wanted to spend time with his son Amir, who was jailed on spying allegations. Ali Hekmati wrote a letter that was personally delivered by a religious leader to Rouhani, a newly elected moderate who is in New York on a closely watched visit to the United Nations, a family spokesman said. \"I ask that you let me see him again, one more time, and so that he may lead our family when I am gone,\" the father wrote. \"Amir is a good man. An honorable man. He is not a spy, I can assure you of that,\" he said. Ali Hekmati said his 30-year-old son wanted to visit his grandmother who could not travel out of Iran. Amir Hekmati, a former Marine, was sentenced to death in January 2012 on charges of espionage. The judiciary later reversed the death sentence, but Hekmati was not among a batch of Iranian political prisoners freed ahead of Rouhani\'s visit. In a recent letter from prison, the younger Hekmati said that he understood that he was being held out of authorities\' hopes that he would be swapped for Iranians held in the United States. The US government and lawmakers have appealed to Iran to free Hekmati, saying it would be a tangible goodwill gesture as Rouhani seeks better relations and a resolution to a row over the clerical regime\'s nuclear program. In the letter, Ali Hekmati acknowledged that the judiciary was a separate institution but urged Rouhani to use his influence to try and secure his son\'s release. The wife of another US citizen jailed separately in Iran, Christian convert Saeed Abedini, said that she handed a letter to Rouhani\'s entourage at a hotel on Monday.