The sister of a former U.S. Marine imprisoned in Iran says her brother renounces his dual Iranian citizenship and vows to never return to the Iran if he's allowed to leave.

Sarah Hekmati said Tuesday that her 31-year-old brother, Amir Hekmati, made the comments in a letter he recently dictated to family members by phone. She says she forwarded it to the office in Pakistan's Washington embassy that represents Iran's U.S. interests.

Hekmati says her brother said he's been "taken hostage" and is being "used as a political bargaining tool."

Arir Hekmati was arrested in August 2011 while visiting relatives in Iran. He was initially convicted of spying and sentenced to death, but that was later overturned and he was sentenced to 10 years in prison on a lesser charge.