A former U.S. Marine being held prisoner in Iran is urging Congress to do more to help free him. 

Amir Hekmati, an Iranian-American with dual citizenship, was arrested while on a trip to Iran to see his ailing grandmother and accused of being an American spy. He was convicted on a lesser charge and sentenced to 10 years in prison.

Greta Van Susteren played the powerful new audio message from Hekmati tonight on "On The Record." 

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“While I am thankful that the State Department and the Obama administration has called for my release and that of my fellow Americans, aside from asking politely, there has been no serious response to this blatant and ongoing mistreatment of Americans by Iran’s Ministry of Intelligence and they continue on with impunity,” Hekmati said in the recording.

Hekmati also asked for his "dignity" to be defended by "putting in place serious consequences for the serial hostage taking and mistreatment of Americans by Iran's Ministry of Intelligence."

Nick Kaywork, a U.S. veteran and friend of Hekmati, told Van Susteren that he sounds "different" than he used to on the recording. 

"You can hear that his resolve is still in his voice in the words that he's using, they're pretty strong words coming over the telephone from Iran," Kaywork said. "But you can definitely hear fatigue, tiredness, something in his voice there ... his well-being is a concern to us."

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Kaywork stated that Iran has dragged Hekmati's family's name through the mud and that his "false imprisonment" is a direct violation of the dignity he has worked to build for his family. 

Hear Hekmati's audio message and see Kaywork's reaction in the clip above.