WASHINGTON - Five Iranian-American groups wrote to US Secretary of State John Kerry last week, urging him to work for the release of an Iranian-American businessman who has been detained in Iran since October.The letter, delivered on Friday, said there was no evidence to justify the detention of Siamak Namazi, who was "left behind" in the wake of a US-Iran prisoner deal that saw other Americans released from Iranian jails last month."An American who has worked tirelessly as a bridge-builder of cultures, countries, and faiths is sitting in a prison in Tehran," said the letter, which was signed by the National Iranian American Council, the Public Affairs Alliance of Iranian Americans and other groups. "We urge you to work tirelessly to pursue Siamak Namazi's release."Namazi, who is based in Dubai, was visiting relatives in Iran when he was detained. Most recently, he was working for Crescent Petroleum, an oil and gas company in the United Arab Emirates, and previously, he headed a consulting firm in Iran."The US government does everything and will continue to do everything it can on behalf of its citizens detained around the world who request our assistance," Sam Werberg, press officer for the State Department's Office of Iranian Affairs, told Reuters by email on Sunday.Namazi's family declined to comment.