DUBAI - A lawyer for an Iranian-American former US Marine jailed in Tehran was reported on Tuesday as saying the United States had sought his release through a prisoner swap, but officials in Washington denied any proposed exchange.Mahmoud Alizadeh Tabatabai, attorney for former Marine Amir Hekmati, told Iran's semi-official Tasnim News Agency that the United States had made the request and it had been put to Iran's judiciary, which has not yet responded."The US has submitted the request via its interest section in Iran," Tabatabai was quoted by Tasnim as saying.Tabatabai did not say which individual or individuals Washington had proposed to release in return for Hekmati's freedom, adding that the names would be made public at the Iranian judiciary's discretion.Reuters telephone calls to Tabatabai's office in Tehran went unanswered. State Department deputy spokesperson Marie Harf said Washington had not suggested a prisoner swap."The USgovernment has not proposed a prisoner exchange for Mr. Hekmati. It is not true," Harf said, calling on the Iranian government to release Hekmati immediately, as well as two other detained US citizens.Hekmati was arrested in August 2011, his family says, and convicted of spying for the CIA, a charge his relatives and the US government deny. His family says he was detained while visiting his grandmother in Tehran.