Iranian-American businessman Siamak Namazi promoted closer ties between his two home countries for years, but now he's the latest source of conflict testing whether President Obama's nuclear deal would be the opening he and his allies hoped would lead to that goal.

News reports said Namazi, head of strategic planning at Dubai-based Crescent Petroleum, was arrested by agents of the Islamic Revolutionary Guard Corps in mid-October while visiting family in Iran. He would be the fourth American held by Iranian authorities. A fifth American, former FBI agent Robert Levinson, went missing in Iran in 2007, and U.S. authorities are seeking information about his fate.

News of Namazi's arrest spurred calls from lawmakers for tougher sanctions against Iran, with many reminding Obama that he had promised to push back against Tehran's bad behavior once the nuclear deal was reached. Specific proposals included listing the IRGC as a terrorist group, which the administration has resisted, and targeted sanctions against the individuals responsible for his arrest.

"Iran's threatening behavior will worsen if the administration does not work with Congress to enact stronger measures to push back, including renewal of the expiring Iran Sanctions Act of 1996 and targeted sanctions against Iran's Revolutionary Guard and against any Iranian official found to have participated in the unjust detainment of American citizens," said Sen. Mark Kirk, R-Ill. Kirk is one of the sponsors of legislation that would impose tougher sanctions on Iran.

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